Storage system and control method for the same

ABSTRACT

An externally-connected volume of a main storage is correlated to an AOU volume inside of an external storage. The AOU volume is allocated with a not-yet-used page in a pool in accordance with data writing. When a command is issued to the externally-connected volume for formatting or others, a first controller in the main storage converts the command into a format command or an area deallocation command with respect to the AOU volume in the external storage. As such, the external AOU volume is subjected to a write process in its entirety, thereby being able to prevent any unnecessary page allocation. With such a configuration, the storage system of the present invention can use pages in the pool with good efficiency.

CROSS REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2008-222601, filed on Aug. 29, 2008, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage system and a control methodfor the storage system.

2. Description of the Related Art

In organizations such as governments, corporations, and universities,for handling a large amount of data varying in type, a storage system ofa relatively large size is used for data management. Such a storagesystem is configured by a disk array device, for example. The disk arraydevice is configured by a large number of storage devices arranged in anarray, and provides a storage area based on, for example, RAID(Redundant Array of. Independent Disks). Any physical storage areaprovided by a group of storage devices as such is formed thereon with atleast one or more logical volumes, which are provided to a hostcomputer, more in detail, to a database program operating on the hostcomputer. The host computer (hereinafter, simply referred to as “host”)can perform data writing/reading to/from the logical volumes withtransmission of any predetermined command.

The data to be managed in the organizations increases in amount day byday, and thus a storage system may be provided with a large storage areain expectation of a demand increase in the future. The issue here isthat, the unit price of a storage device indeed tends to be reduced yearby year, but purchasing a large number of storage devices to be readyfor a demand increase in the future as such may result in excessiveupfront investment. Therefore, when the need arises for any new storagearea, purchasing any appropriate number of storage devices willfavorably reduce the cost of the storage system.

On the other hand, if a storage area satisfying only the current demandis available for use, any new demand cannot be immediately met, therebyreducing the usability of the storage system. In consideration thereof,Patent Document 1 (JP-A-2005-31929) describes a technology ofvirtualizing, for management, storage areas of storage devices in astorage system, and using the virtualized storage areas as needed.

Moreover, for using any existing storage resources with good efficiency,Patent Document 2 (JP-A-2005-107645) describes a technology with whichone storage control device captures thereinto a logical volume(s) inanother storage control device, and makes a host believe that thelogical volume(s) are of its own. In this previous technology, thecorrelation is controlled between a logical volume(s) being a connectionsource and a logical volume(s) being a connection destination, and inaccordance with an access made to the logical volume (s) being theconnection source, another access is made to the logical volume(s) beingthe connection destination.

SUMMARY OF THE INVENTION

If a technology for virtualization of storage capacity is combinedtogether with a technology for virtualization of storage controldevices, a logical volume(s) being a connection destination may beunnecessarily accessed for writing with a high frequency, therebypossibly reducing the use efficiency of a storage area. Exemplifiedbelow is a case where a logical volume(s) being a connection destinationare configured as a logical volume(s) of using a physical storage areain a pool as needed, and a logical volume(s) being a connection sourceare subjected to a format process.

In this case, every logical volume being a connection destination issubjected to a process for writing of format data, and it means thatevery logical volume being the connection destination is allocated withthe storage area in the pool. With the storage area in the pool beingunnecessarily allocated to the logical volumes each being a connectiondestination as such, this thus causes a problem of not being able to usethe storage area in the storage system with good efficiency. The storagesystem also suffers from unnecessary traffic.

The invention is proposed in consideration of such problems, and anobject thereof is to provide a storage system that enables the effectiveuse of storage resources, and a control method for the storage system.Another object of the invention is to provide a storage system that cansuppress the frequency of a write access to a second volume, and acontrol method for the storage system. Other objects of the inventionwill become more apparent from the following detailed description of theinvention.

The invention has the following typical aspects to solve the problemsabove. A first aspect of the invention is directed to a storage systemin which first and second storage control devices are connected to eachother for communications, including: a first volume that is providedvirtually to the first storage control device; a second volume that isprovided virtually to the second storage control device withcorrespondence in terms of a storage space with the first volume, and isaccessed in response to an access request to the first volume; a poolsection that keeps a plurality of physical storage areas for allocationto the second volume in response to a write access request to the secondvolume; a first control section that is provided to the first storagecontrol device, issues a command to the second volume in response to theaccess request to the first volume, and performs data reading/writingfrom/to the second volume; and a second control section that is providedto the second storage control device, performs data input/output to/fromthe second volume in response to the command coming from the firstcontrol section, and allocates, to the second volume, in response to awrite access request coming from the first control section, any of theplurality of physical storage areas in the pool section not yet in use.In the storage system, when receiving a first predetermined commandabout the first volume, the first control section converts, fortransmission to the second control section, the first predeterminedcommand into a second predetermined command to relatively reduce a writeaccess frequency to the second volume.

The components, functions, and steps of the invention may be possiblyconfigured as a computer program to be run by a computer system. Whenthe configuration of the invention is implemented entirely or partiallyby such a computer program, this computer program can be distributed invarious types of storage media or transmitted over a communicationsnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the outline of an embodiment of theinvention;

FIG. 2 is a diagram showing the entire configuration of a storagesystem;

FIG. 3 is a block diagram of the storage system;

FIG. 4 is a diagram showing the functional components of eachcontroller;

FIG. 5 is a diagram showing the storage configuration of the storagesystem;

FIG. 6 is a diagram showing the hierarchical relationship in eachstorage configuration;

FIG. 7 is a diagram showing an LDEV management table, and others;

FIG. 8 is a diagram showing a VDEV/EDEV management table, and others;

FIG. 9 is a diagram showing an internal AOU volume management table, andothers;

FIG. 10 is a diagram showing a page-state combination table, and others;

FIG. 11 is a diagram showing a pool volume management table;

FIG. 12 is a diagram showing a local copy pair management table;

FIG. 13 is a diagram showing a remote copy pair management table;

FIG. 14 is a diagram showing a table for use to manage functions of anexternal storage;

FIG. 15 is a flowchart of an external connection setting process;

FIG. 16 is a flowchart of a pool volume setting process;

FIG. 17 is a flowchart of a format process;

FIG. 18 is a flowchart of a format process to be executed to internalphysical volumes;

FIG. 19 is a flowchart of a format process to be executed to internalAOU volumes;

FIG. 20 is a flowchart of a format process to be executed to externalphysical volumes;

FIG. 21 is a flowchart of a format process to be executed to externalAOU volumes;

FIG. 22 is a flowchart of a shred process;

FIG. 23 is a flowchart of a shred process to be executed to the internalphysical volumes;

FIG. 24 is a flowchart of a shred process to be executed to the internalAOU volumes;

FIG. 25 is a flowchart of a shred process to be executed to the externalphysical volumes;

FIG. 26 is a flowchart of a shred process to be executed to the externalAOU volumes;

FIG. 27 is a flowchart of a write process to be executed to datavolumes;

FIG. 28 is a flowchart of a pair formation copy process;

FIG. 29 is a flowchart of a pair resync copy process;

FIG. 30 is a flowchart of a pair restore copy process;

FIG. 31 is a diagram showing the configuration of each controller in astorage system of a second example;

FIG. 32 is a diagram showing an update management table;

FIG. 33 is a diagram showing a VDEV/EDEV management table;

FIG. 34 is a flowchart of an external connection setting process;

FIG. 35 is a flowchart of a write process to be executed toexternally-connected volumes;

FIG. 36 is a diagram showing how a format pattern is embedded into aportion in an update management size not written with write data;

FIG. 37 is a flowchart of a process for data reading from externalvolumes;

FIG. 38 is a flowchart of a format process to be executed to externalAOU volumes;

FIG. 39 is a flowchart of a format process to be executed to externalphysical volumes;

FIG. 40 is a flowchart of a write process to be executed to internalphysical volumes;

FIG. 41 is a flowchart of a process for data reading from internalphysical volumes;

FIG. 42 is a flowchart of a format process to be executed to theinternal physical volumes;

FIG. 43 is a flowchart of a format process to be executed to theinternal physical volumes;

FIG. 44 is a flowchart of a pair formation copy process;

FIG. 45 is a flowchart continued from the flowchart of FIG. 44;

FIG. 46 is a flowchart of an external connection setting process to beexecuted in a storage system of a third example;

FIG. 47 is a flowchart of a write process to be executed to data volumesin a storage system of a fourth example;

FIG. 48 is a flowchart of a process for page deallocation in internalAOU volumes;

FIG. 49 is a flowchart of a process for page deallocation in externalAOU volumes;

FIG. 50 is a flowchart of a pair formation copy process;

FIG. 51 is a flowchart of a data comparison process;

FIG. 52 is a diagram showing a storage system of a fifth example in itsentirety;

FIG. 53 is a diagram showing the storage configuration of the storagesystem;

FIG. 54 is a diagram showing a storage system of a sixth example in itsentirety; and

FIG. 55 is a diagram showing the storage configuration of the storagesystem.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a diagram showing the general configuration of a storagesystem in an embodiment of the invention. As will be described later,this system utilizes an external connection function, and an AOU(Allocation On Use) function. The external connection function is foruse to make a host 3 believe that a volume 8 actually located outside ofa main storage 1 is located inside of the main storage 1, i.e., forvirtualizing storage control devices. Note that FIG. 1 merely showsschematically only one aspect of the invention, and the scope of theinvention is not intentionally limited to the configuration of FIG. 1.

The AOU function is for use to allocate, at the time of data writing tological volumes, any of physical storage areas managed in a pool to anarea being a write target of data, i.e., for virtualizing storagecapacity.

The storage system of this embodiment is configured to include at leastone or more main storages 1, at least one or more external storages 2,and at least one or more hosts 3, for example. This storage system maybe also provided with a device for management use, e.g., managementserver 20 of FIG. 2.

The main storage 1 is corresponding to a “first storage control device”.The main storage 1 plays a leading role in the storage system. The host3 utilizes storage resources in the storage system via the main storage1. The main storage 1 is configured to include a first controller 4 as a“first control section”, an AOU volume 6 generated by utilizing the AOUfunction, an externally-connected volume 7 as a “first volume”, and anAOU pool PL1, for example.

The first controller 4 controls the operation of the main storage 1. Thefirst controller 4 is provided with a function 4A for IO (Input/Output)processing, a function 4B for control over AOU, a function 4C forcontrol over external connection, a function 4D for command conversion,and update bitmaps 4E and 4F each as update management information.

With the IO processing function 4A, data reading/writing is performedfrom/to the AOU volume 6 and the externally-connected volume 7 inresponse to a write command, a read command, and others provided by thehost 3. With the AOU control function 4B, the AOU pool PL1 and the AOUvolume 6 are controlled. With the AOU control function 4B, when arequest comes from the host 3 for data writing to any new area, anynot-in-use page in the AOU pool PL1 is allocated to the AOU volume 6.This page corresponds to a “physical storage area”. In any predeterminedcase, also with the AOU control function 4B, the page having beenallocated to the AOU volume 6 is deallocated, and the page is put backto the AOU pool PL1.

With the external connection control function 4C, based on thecorrelation between the externally-connected volume 7 and the externalvolume 8 in the external storage 2, a command directed to theexternally-connected volume 7 is converted into a command to the volume8 in the external storage 2.

The externally-connected volume 7 is the one correlated to the volume 8in the external storage 2. Therefore, the externally-connected volume 7may be also referred to as connection-source volume orexternally-connected volume connected to any external volume. The volumein the external storage 2 is referred to as external volume orconnection-destination volume.

The external connection control function 4C manages the correlation interms of a storage space between the externally-connected volume 7 beingthe connection-source volume and the external volume 8 being theconnection-destination volume. The external connection control function4C also manages access path information about an access to the externalvolume 8, for example. When the host 3 issues a write command to theexternally-connected volume 7, for example, with the external connectioncontrol function 4C, the write command is converted into a write commandto the external volume 8. The resulting write command after conversionas such is forwarded to a second controller 5 in the external storage 2.In this manner, the host 3 is made to believe that it is performing datawriting to the externally-connected volume 7 in the main storage 1, butthe actual data is stored in the external volume 8 in the externalstorage 2.

With the command conversion function 4D, among commands issued towardthe externally-connected volume 7, a predetermined command is convertedinto any other command. For example, the following commands, e.g.,format command, shred command, volume copy command, resync command, andrestore command, are each corresponding to a “first predeterminedcommand”.

With the command conversion function 4D, the first predetermined commandis converted into a second predetermined command for the purpose ofrelatively reducing the frequency of a write access to the externalvolume 8. The second predetermined command as a result of conversion assuch is forwarded to the second controller 5. With the commandconversion function 4D, when a format command asking for formatting ofthe externally-connected volume 7 (9A), for example, if possible, theformat command is converted into either a command asking for formattingof the AOU external volume 8, or a command asking for deallocation ofany page having been allocated to the AOU external volume 8 (9C).

When such a command for formatting or page deallocation to the AOUexternal volume 8 cannot be issued by the first controller 4, with thecommand conversion function 4D, a write command is issued as“alternative command” for writing of format data into the AOU externalvolume 8. The format data corresponds to “predetermined data”.

With the command conversion function 4D, when a command is provided forestablishing synchronization of storage details between theexternally-connected volume 7 and the AOU external volume 8 (9B), only adifference of storage details between the externally-connected volume 7and the AOU external volume 8 is written into the AOU external volume 8(9D). Note that such command processing will be described in detaillater.

The update bitmap 4E corresponds to “first management information”, andthe update bitmap 4F corresponds to “second management information”. Theupdate bitmap 4E manages the state of use of the volumes 6 and 7 in themain storage 1. The update bitmap 4F manages the state of use of theexternal volume 8 in the external storage 2. With the IO processingfunction 4A, these update bitmaps 4E and 4F are updated based on thewrite command provided by the host 3, for example.

Described now is the external storage 2 as “second storage controldevice”. As is located outside of the main storage 1, the externalstorage 2 is referred to herein as “external storage”. The externalstorage 2 is configured to include the second controller 5 as “secondcontrol section”, the AOU external volume 8 as “second volume”, and anAOU pool PL2 as “pool section”, for example.

The second controller 5 controls the operation of the external storage2. The second controller 5 is provided with an IO processing function5A, and an AOU control function 5B, for example. With the IO processingfunction 5A, data reading/writing is performed from/to the AOU externalvolume 8 in response to a command coming from the first controller 4,and the result of data reading/writing as such is forwarded as aresponse to the first controller 4. Similarly to the AOU controlfunction 4B of the first controller 4, the AOU control function 5Bperforms control over the AOU pool PL2 and the AOU external volume 8.

Similarly to the AOU volume 6 in the main storage 1, the AOU externalvolume 8 is virtually generated. The AOU external volume 8 is anexternal volume located inside of the external storage 2, and is avolume configured by AOU. For data writing to such an AOU externalvolume 8, a page in the AOU pool PL2 is allocated to the AOU externalvolume 8.

In this embodiment in which the storage system is configured as such,the externally-connected volume 7 in the main storage 1 is correlatedwith the AOU external volume 8 in the external storage 2, therebyallowing effective use of storage resources in the storage system. Bythe main storage 1 capturing thereinto the external volume 8 of theexternal storage 2, the volumes scattered in the storage system can bevirtualized and managed. Moreover, by using the AOU volumes 6 and 8 eachallocated with a page in accordance with the actual state of use, thephysical storage areas, i.e., pages, can be used with good efficiency.

Also in this embodiment, when the command directed to theexternally-connected volume 7 is the first predetermined command, thecommand is converted into a second predetermined command with which thefrequency of a write access to the AOU external volume 8 is relativelyreduced, and the resulting command is forwarded to the second controller5. This thus favorably prevents the AOU external volume 8 from beingallocated with any unnecessary page, thereby allowing effective use ofthe storage resources, i.e., pages, in the external storage 2. In thebelow, this embodiment is described in more detail.

First Example

FIG. 2 is a diagram showing the entire configuration of a storage systemin a first example. Components in the storage system of FIG. 2 arecorrelated to those in the storage system of FIG. 1, and theircorrelation is described first. That is, a host 10 is correlated to thehost 3 of FIG. 1, a main storage 100 to the main storage 1 of FIG. 1, anexternal storage 200 to the external storage 2 of FIG. 1, a firstcontroller 110 to the first controller 4 of FIG. 1, and a secondcontroller 210 to the second controller 5 of FIG. 1.

The storage system is configured to include at least one host 10, atleast one main storage 100, at least one or more external storages 200,and the management server 20 connected to each of the storages 100 and200, for example.

The host 10 is a computer device provided with information processingresources such as CPU (Central Processing Unit) and memory, and isconfigured as a personal computer, a work station, a main frame, aserver computer, and others. The host 10 is connected to the mainstorage 100 over a communications network CN1 such as SAN (Storage AreaNetwork) and LAN (Local Area Network).

The main storage 100 plays a main role in the storage system. Althoughthe details are left for later description, the main storage 100 can beconfigured to include the controller 110 and a storage deviceincorporated section 120. The main storage 100 is connected to each ofone or more hosts 10 over the communications network CN1. The mainstorage 100 is also connected to each of one or more storages 200 overanother communications network CN2. The communications network CN2 canbe exemplified for use by an IP-SAN (Internet Protocol in Storage AreaNetwork) utilizing an IP protocol, or an FC-SAN (Fibre Channel inStorage Area Network) utilizing an FC protocol, for example.

The external storage 200 is located outside of the main storage 100. Theexternal storage 200 is configured to include the second controller 210,and a storage device incorporated section 220. As will be describedlater, the external storage 200 can provide a physical or AOU volume tothe main storage 100.

The management server 20 manages the state of each of the storages 100and 200. The management server 20 is connected to each of the storages100 and 200 over a communications network CN3 such as LAN, for example.The management server 20 serves to collect information from the storages100 and 200, and issue commands thereto. Alternatively, the managementserver 20 may be so configured as to be able to communicate with thestorages 100 and 200 over the communications network CN2 between thestorages.

FIG. 3 is a block diagram of the storage system. Due to limited space,FIG. 3 mainly shows the configuration of the main storage 100. The host10 is configured to include an HBA (Host Bus Adapter) 11 forcommunications with the main storage 100, and a management program 12for management of the main storage 100, for example.

The main storage 100 is configured as a disk system including a harddisk device and a flash memory device, for example. This is surely notrestrictive, and the main storage 100 may be configured as ahigh-performance intelligent switch or a virtualized appliance for useto virtualize a plurality of storages.

As described above, the main storage 100 is mainly configured by thefirst controller 110, and the storage device incorporated section 120.The first controller 110 is configured to include a plurality of channeladapters 111, a plurality of disk adapters 112, a cache memory 113, ashared memory 114, and a connection control section 115, for example.For convenience, the channel adapters are each abbreviated to CHA, thedisk adapters to DKA, the cache memory to CM, the shared memory to SM,and the connection control section to SW.

The one or more CHAs 111 are provided for data communications with thehost 10. The one or more CHAs 111 are provided with a communicationsport 111T (target port) for communications with the host 10, and anyother one or more CHAs 111 are provided with a communications port 111Efor communications with the external storage 200.

Such CHAs 111 are each configured as a microcomputer system providedwith a CPU, a memory, and others, and interpret and execute varioustypes of commands provided by the host 10. The CHAs 111 are eachallocated with a network address for identification use, e.g., IPaddress and WWN (World Wide Name).

The DKAs 112 are provided for data exchange with disk drives 121 in thestorage device incorporated section 120. Similarly to the CHAs 111, theDKAs 112 are each configured as a microcomputer system provided with aCPU, a memory, and others. The DKAs 112 each perform data writing to anypredetermined address of any predetermined one of the disk drives 121.The data to be written here is the one provided to the CHAs 111 by thehost 10. The DKAs 112 also each read data from any predetermined addressof any predetermined one of the disk drives 121, and forward the readingresult to the host 10 or the external storage 200.

For data input/output with the disk drives 121, the DKAs each convert alogical address into a physical address. When the disk drives 121 aremanaged based on RAID, the DKAs each make a data access in accordancewith the RAID configuration. For example, the DKAs 112 each write thesame data into each different disk drive groups, i.e., RAID groups.Alternatively, the DKAs 112 each perform parity calculation, and thenperform writing of data and the resulting parity into the disk drivegroups.

The cache memory 113 temporarily stores data provided by the host 10 orthe external storage 200, or temporarily stores data read from the diskdrives 121.

The shared memory (also referred to as control memory) stores varioustypes of control information for use to operate the main storage 100,for example. The shared memory is set with a work area, and also storesvarious types of tables that will be described later. The configurationof the tables will be described later. The storage details of the tablescan be copied entirely or partially into the CHAs 111 and the DKAs 112,respectively.

Alternatively, any one or more of the disk drives 121 may be used asdisks for cache use. Still alternatively, the cache memory 113 can beconfigured separately from the shared memory 114, or in a memory, anypart of the storage area may be used as a cache area, and any other partthereof may be used as a control area.

The connection control section 115 serves to establish a connectionamong the CHAs 111, the DKAs 112, the cache memory 113, and the sharedmemory 114. The connection control section 115 can be configured as acrossbar switch or a bus that performs data transmission by a high-speedswitching operation, for example.

The storage device incorporated section 120 is provided with a pluralityof disk drives 121. In the below, the storage device incorporatedsection is abbreviated to HDU (Hard Disk Unit). The storage device canbe exemplified by various types of data readable/writable devices suchas hard disk device, semiconductor memory device, optical disk device,magneto-optical disk device, magnetic tape device, and flexible diskdevice.

When the storage device is a hard disk device, possibly used are an FC(Fibre Channel) disk, an SCSI (Small Computer System Interface) disk, anSATA (Serial ATA) disk, an ATA (AT attachment) disk, an SAS (SerialAttached SCSI) disk, and others. When the storage device is asemiconductor memory device, possibly used are a flash memory, a FeRAM(Ferroelectric Random Access Memory), an MRAM (Magnetoresistive RandomAccess Memory), an Ovonic Unified Memory, a RRAM (Resistance RAM), andothers.

A service processor 116 serves to collect various types of informationfrom inside of the main storage 100, and write control information intothe shared memory 114, for example. Such information collection andwriting are performed over an internal communications network CN4 suchas LAN. In the below, the service processor 116 is abbreviated to SVP.In the drawing, exemplified is a case where the SVP 116 is connected toeach of the CHAs 111. This is surely not restrictive, and thecommunications network CN4 may connect together the SVP 116, the CHAs111, and the DKAs 112.

The management server 20 is connected to the SVP 116 in the main storage100, and an SVP 230 in the external storage 200 over a communicationsnetwork such as LAN. The management server 20 is provided with a storagemanagement section 21A, which is software for management of the storages100 and 200. The management server 20 collects various types ofinformation about the main storage 100, or issues various types ofcommands to the main storage 100 over the SVP 116.

As described above, the external storage 200 is provided with the secondcontroller 210, and the HDU 220. The external storage 200 is connectedto the main storage 100 via a communications port 211. The externalstorage 200 can be of the configuration almost the same as that of themain storage 100. Alternatively, the external storage 200 may be simplerin configuration than the main storage 100. The HDU 220 of the externalstorage 200 is provided with a plurality of disk drives 221. These diskdrives 221 each provide a physical storage area, which is sometimeshandled as an internal storage area of the main storage 100.

FIG. 4 is a diagram showing the functional configuration of the storagesystem. The first controller 110 is configured to include a firstcommunications processing section 101, an IO processing section 102, anexternal connection control section 103, an AOU control section 104, anexternal storage operation section 105, and a second communicationsprocessing section 106, for example.

The first communications processing section 101 is a function for use toperform data communications with the host 10, which is a high-enddevice. The second communications processing section 106 is a functionfor use to perform data communications with the disk drives 121, whichare each a low-end device. The IO processing section 102 is a functionfor use to perform data reading/writing in accordance with a commandcoming from the host 10, and forward back the result.

As will be described later, the external connection control section 103performs control over any virtual logical volume (externally-connectedvolume) in the main storage 100, and any logical volume in the externalstorage 200 (external volume) through correlation therebetween.

The AOU control section 104 controls the AOU volume (internal AOUvolume) in the main storage 100. The external storage operation section105 serves to issue, to the external storage 200, a format command, anarea deallocation command, and others.

The second controller 210 is configured to include a firstcommunications processing section 201, an IO processing section 202, anAOU control section 203, and a second communications processing section204, for example. The first communications processing section 201 is afunction for use to perform data communications with the main storage100, which is a high-end device. The second communications processingsection 204 is a function for use to perform data communications withthe disk drives 221. The IO processing section 202 performs datareading/writing in accordance with a command provided by the firstcontroller 110, and forwards the result back to the first controller 110as a response. The AOU control section 203 controls the AOU volume inthe external storage 200.

FIG. 5 is a diagram schematically showing the storage configuration ofthe storage system. The storage configuration of the main storage 100 isbroadly divided into a physical storage hierarchy, and a logical storagehierarchy. The physical storage hierarchy is configured by the diskdrives 121 each being a physical disk PDEV (Physical DEVice).

The logical storage hierarchy can be provided plurally. The one logicalhierarchy is a VDEV (Virtual DEVice)/EDEV (Expand virtual DEVice) layer,another logical hierarchy is an LDEV (Logical Device) layer, and stillanother logical hierarchy is an LU (Logical Unit) layer.

A VDEV 122V is configured by a group of a plurality of disk drives 121,e.g., a group of four (3D+1P), or a group of eight (7D+1P). The diskdrives 121 of a group each provide a storage area, and the combinedstorage area form a RAID storage area. This RAID storage area is theVDEV 122V.

Herein, not every VDEV is generated directly on the physical storagearea (PDEV), and at least a part of the VDEVs is configured as an EDEV122E, which is a virtual intermediate storage device. The EDEV 122E isused for mapping of LUs (Logical Units) 224 of the external storage 200.

An LDEV 123 is a logical volume, and the VDEV 122V or the EDEV 122E canbe provided thereon with at least one or more LDEVs 123. Alternatively,a plurality of VDEVs 122V or EDEVs 122E may be collectively correlatedto one LDEV 123.

When the host 10 is a so-called open host, by the LDEV 123 being mappedto an LU 124, the host 10 acknowledges the LDEV 123 as a physical disk.The open host accesses any desired LDEV 123 through designation of LUN(Logical Unit Number) or logical block address. Herein, when the host 10is a so-called mainframe host, the host 10 directly acknowledges theLDEV 123.

Among the LDEVs 123, any virtually-generated AOU volume 123A (refer toFIG. 6) is correlated to an AOU pool 122P. Hereinafter, the AOU pool maybe sometimes simply referred to as pool. Externally-connected volume123E (refer to FIG. 6) out of the LDEVs 123 is connected to a logicalvolume in the external storage 200. An externally-connected volume 123Eis correlated to the LU 224 of the external storage 200 via the EDEV122E.

The LU 124 is a device acknowledgeable as a logical unit of the SCSI.The LU 124 is connected to the host 10 via the target port 111T. The LU124 can be correlated with at least one or more LDEVs 123. By one LU 124being correlated with a plurality of LDEVs 123 as such, the LU can bevirtually increased in size.

Alternatively, any special-purpose device called CMD (Command Device)may be provided. The CMD is used for command or status exchange betweenthe program operating on the host 10 and the first controller 110 of themain storage 100.

An initiator port (External Port) 111E in the main storage 100 forexternal connection use is connected with the external storage 200 overthe communications network CN2. The external storage 200 is providedwith a plurality of disk drives 221, a VDEV 222 set on the storage areasprovided by the disk drives 221, and at least one or more LDEVs 223 thatcan be set on the VDEV 222. The LDEVs 223 are correlated to the LUs 224,respectively. The LDEVs 223 in this external storage 200 are eachcorrelated to the externally-connected volume 123E, thereby providing aphysical storage area to the externally-connected volume 123E.

FIG. 6 is now referred to. FIG. 6 is a diagram showing an exemplaryrelationship between the storage hierarchies. The AOU volume 123A foundat the left end of FIG. 6 is correlated to the pool 122P.

The pool 122P manages the physical storage area of a pool volume 123P.When the host 10 writes data to any not-in-use portion of the AOU volume123A, a not-in-use page under the management of the pool 122P isallocated to the AOU volume 123A. Data for writing provided by the host10 is stored into thus allocated page.

The pool 122P can accommodate therein various types of volumes, i.e.,first to third 123P(1) to 123P(3). The first pool volume 123P(1) is aphysical volume in the main storage 100. That is, the first pool volume123P is formed based on the disk drives 121 in the main storage 100. Thesecond pool volume 123(2) is utilizing an LDEV 223R in the externalstorage 200. That is, the second pool volume 123P(2) is anexternally-connected volume connected to the external volume in theexternal storage 200. The third pool volume 123P(3) is a volume to beconnected to an AOU volume 223A in the external storage 200. That is,the third pool volume 123P(3) is also an externally-connected volume.

At the right side of the pool 122P, the externally-connected volume 123Eis shown. The externally-connected volume 123E is connected to the AOUvolume 223A in the external storage 200 via the EDEV 122E. Data forwriting to the externally-connected volume 123E is stored in theexternal volume in the external storage 200. The externally-connectedvolume 123E may be of the same size as the external volume in theexternal storage 200, e.g., the volume 223R or 223A in FIG. 6 example.Data for writing with which any predetermined address of theexternally-connected volume 123E is designated is stored in anycorresponding address in the external volume, i.e.,connection-destination volume, in the external storage 200. When theconnection-destination volume is the AOU volume 223A, data for writingthereto is stored into the page in the pool 222P allocated to the AOUvolume 223A.

On the right end of FIG. 6, a general physical volume 123R is shown. Thephysical volume 123R is connected to a PDEV 121 in the main storage 100via the VDEV 122V.

As shown in the lower-side portion of FIG. 6, the external storage 200is also provided with the physical volume 223R and the AOU volume 223A.The physical volume 223R is correlated to a PDEV 221 in the externalstorage 200. The AOU volume 223A is correlated to the page in the pool222P. The pool 222P accommodates therein at least one or more poolvolumes 223P.

Described next is configuration examples of various tables andinformation to be used in the storage system. FIG. 7 shows an LDEVmanagement table T10, a volume type combination table T11, and a volumestate management table T12. These management tables T10 to T12 are allstored in the shared memory 114 in the first controller 110.

For convenience, in the drawing, volumes are abbreviated to VOLs. Thevolumes are the LDEVs. The physical VOLs are those correlated to thePDEVs, i.e., physical storage devices. An AOU-VOL denotes a volumeformed by allocation of a page managed in a pool.

The internal volume is a volume existing in the main storage 100. Theexternal volume is a volume found inside of the external storage 200.The externally-connected volume is a volume located inside of the mainstorage 100, but the actual storage destination thereof is located inthe external volume.

The LDEV management table T10 is used for managing the volumes (LDEVs)under the direct or indirect management of the main storage 100. Thetable T10 includes fields of LDEV-ID, size, type of volume, state ofvolume, volume pair, corresponding LU, and corresponding VDEV, forexample.

The “LDEV-ID” is identification information for use to identify each ofthe LDEVs in the storage system. The “size” indicates the size of eachof the LDEVs. The “type of volume” indicates the type of each of theLDEVs. The “state of volume” indicates the state of each of the LDEVs.To any of the LDEVs, when a local copy pair or a remote copy pair thatwill be described later is set, the “volume pair” is set with a pair IDfor pair identification.

The “corresponding LU” is set with identification information for use toidentify the LU correlated to the LDEV. The “corresponding VDEV” is setwith identification information for use to identify the VDEV or EDEVcorrelated to the LDEV.

The volume type combination table T11 shows combinations of volumes(LDEVs) varying in attribute. The volumes in the storage system arebroadly classified into data volumes and pool volumes. The data volumesare those provided to the host 10 via the corresponding LU. The poolvolumes are those for providing storage areas for allocation to the AOUvolumes, and are managed by the pools.

The data and pool volumes can be each configured by a physical volume oran AOU volume. The data volume can be configured by a physical volume oran AOU volume. The pool volume can be also configured by a physicalvolume or an AOU volume.

The physical and AOU volumes can be all broadly classified into internalvolumes or externally-connected volumes. The volume correlated to thePDEV inside of the storage is an internal volume. The volume to becorrelated to the PDEV located outside of the storage is anexternally-connected volume.

The volume state management table T12 manages the state of volumes. Themanagement table T12 manages fields of state of use, state of format,state of shred, and state of writing, for example.

The “state of use” indicates whether the volume is being used normallyor not. When the volume is used normally, “normal” is set to the volume.When the volume is not used normally, “closed” is set to the volume.

The “state of format” indicates the state of the volume related toformatting. When the volume is not yet formatted, “Not yet formatted” isset to the volume. When the volume is being formatted, “duringformatting” is set to the volume. When the volume is already formatted,“formatted” is set to the volume.

The “state of shred” indicates the state of the volume related toshredding. The shredding denotes a process for completely deleting datastored in the volume by writing any predetermined shred data for aplurality of times to the data stored in the volume. When the volume isduring such a shred process, “during shredding” is set to the volume.When the volume is not during the shred process, “not during shredding”is set to the volume.

The “state of writing” indicates the state of data writing to thevolume. When the volume is being written with data, “Yes” is set to thevolume. When the volume is not being written with data, “No” is set tothe volume.

FIG. 8 is a diagram showing a VDEV/EDEV management table T13, a devicegroup management table T14, and a PDEV management table T15. TheVDEV/EDEV management table T13 is used for managing any intermediatestorage devices, i.e., VDEVs and EDEVs. The management table T13 managesfields of VDEV-ID/EDEV-ID, size, type, state, RAID configuration,corresponding LDEV, and corresponding device group/correspondingconnection-destination volume, for example.

The “VDEV-ID/EDEV-ID” is identification information for use to identifythe VDEV and EDEV. The VDEV is used for generating an LDEV based on aphysical storage area inside of the storage. The EDEV is used forgenerating an LDEV based on a physical storage area outside of thestorage.

The “size” indicates the storage capacity of the VDEV and that of EDEV.The “type” indicates the type of the VDEV and that of EDEV. The type isexemplified by the type of a PDEV, e.g., ATA disk and flash memorydevice, correlated to the VDED and EDEV. The “state” indicates whetherthe VDEV and EDEV are operating normally or not.

The “RAID configuration” indicates the type of RAID configuration of theVDEV and EDEV. The “corresponding LDEV” is set with information for useto identify the LDEV, i.e., LDEV-ID, correlated to the VDEV and EDEV.The “corresponding device group/corresponding external volume” is setwith information for accessing a device group or an external volumecorrelated to the VDEV and LDEV. With the VDEV, information about thedevice group corresponding to the VDEV is set, and with the EDEV,information for accessing the external volume connected to the EDEV,i.e., connection-destination volume, is set. The information for anaccess as such is exemplified by port number, WWN, LU number, andothers.

The device group management table T14 manages the device groups. Thedevice groups are those of the PDEVs configuring the VDEV. Themanagement table T14 manages fields of device group ID, state, RAIDconfiguration, corresponding VDEV, and corresponding PDEV, for example.

The “device group ID” is information for use to identify each of thedevice groups. The “state” indicates whether the device group isoperating normally or not. The “RAID configuration” indicates the RAIDconfiguration of the device group. The “corresponding VDEV” identifiesthe VDEV correlated to the device group. The “corresponding PDEV”identifies the PDEV included in the device group. For identifying thePDEV configuring the device group, the PDEV-ID is set.

The PDEV management table T15 is used for managing the PDEVs. Themanagement table T15 manages fields of PDEV-ID, size, state, andcorresponding VDEV, for example.

The “PDEV-ID” is identification information for use to identify each ofthe PDEVs. The “size” indicates the storage capacity of the PDEV. The“state” indicates whether the PDEV is operating normally or not. Whenthe PDEV is operating normally, for example, a setting is made as“normal”, and when some problem is occurred to the PDEV, a setting ismade as “abnormal”. When the PDEV is not operating due to power saving,a setting is made as “power saving”. The “corresponding VDEV” identifiesthe VDEV correlated to the PDEV.

FIG. 9 is a diagram showing an internal AOU volume management table T16,an internal AOU pool management table T17, an allocation page managementtable T18, and an internal AOU page management table T19.

The internal AOU volume management table T16 is used for managing theAOU volumes inside of the storage. The management table T16 managesfields of AOU pool ID, and allocation page information, for example.

The “AOU pool ID” is information for use to identify the AOU poolcorrelated to the AOU volume. The “allocation page information” isinformation for use to manage the page correlated to the AOU volume.

The internal AOU pool management table T17 is used for managing the AOUpools inside of the storage. The management table T17 manages fields ofAOU pool ID, pool volume information, AOU volume list, and pageinformation, for example.

The “AOU pool ID” indicates information for use to identity the AOUpool. The “pool volume information” is information indicating the poolvolume(s) included in the AOU pool. The pool volume information includessub-fields of “number of volumes” and “list of volumes”. The “number ofvolumes” indicates the total number of the pool volumes found in the AOUpool, and the “list of volumes” indicates the list of the pool volume(s)found in the AOU pool.

The “list of AOU volumes” indicates the list of the AOU volume(s)correlated to the AOU pool. The “page information” indicates theinformation about each of the pages found in the AOU pool. The pageinformation includes, for example, sub-fields of “size”, “total numberof pages”, “number of vacant pages”, and “pointer”.

The “size” indicates the storage size of each of the pages. That is, the“size” indicates the minimum configuration unit of the AOU volume. The“total number of pages” indicates the total number of pages found in theAOU pool. The “number of vacant pages” indicates the number of pages notyet used in the AOU pool. The “pointer” points any applicable portion inthe allocation page management table.

The allocation page management table T18 is used to manage the pagesentered in the AOU pool. The management table T18 manages fields ofstart address, allocation status, and page ID, for example.

The “start address” indicates the start address of the page. The endaddress of the page can be found by adding the page size to the value ofthe start address. The “allocation status” indicates whether the page isallocated to the AOU volume or not. When the page is not allocated tothe AOU volume, “Not yet” is set, and when the page is allocated to theAOU volume, “Done” is set. The “page ID” is identification informationfor use to identify the page.

The internal AOU page management table T19 is used to manage the pagesconfiguring the AOU volumes inside of the storage. The management tableT19 manages fields of page ID, page state, pool volume, and AOU volume,for example.

The “page ID” is identification information for use to identify the pageallocated to the AOU volume. The “page state” indicates the state of thepage. The page state includes sub-fields of “state of allocation” and“state of initialization”. As shown in FIG. 10, the “state ofallocation” is set with “Done” when the page is allocated to the AOUvolume, and is set with “Not yet” when the page is not allocated to theAOU volume. The “state of initialization” indicates whether the page isinitialized or not. As shown in FIG. 10, when the initializationprocess, i.e., format process, is completed, a setting is made as“Done”, and when the initialization process is not yet done, a settingis made as “Not yet”.

FIG. 9 is referred back to. The “pool volume” manages the pool volumefrom which the page is provided. The pool volume includes sub-fields of“LDEV-ID” and “start address”. The “LDEV-ID” is information for use toidentify the pool volume from which the page is provided. The “startaddress” indicates where the page starts in the pool volume.

The “AOU volume” is the field for use to manage the AOU volume to whichthe page is allocated. The AOU volume includes sub-fields of “LDEV-ID”and “start address”. The “LDEV-ID” is information for use to identifythe AOU volume to which the page is allocated. The “start address”indicates the address inside of the AOU volume to which the page isallocated, i.e., indicates which area of the AOU volume the page istaking in charge in the storage.

FIG. 10 is a diagram showing a page state combination table T20, and apage state change table T21. As described by referring to the managementtable T19 of FIG. 9, the state of allocation shows two states of “Done”and “Not yet” for a page, and the state of initialization also shows twostates of “Done” and “Not yet” for a page. As such, for a page, thereare four combination patterns between the state of allocation and thestate of initialization.

When the page is not yet allocated, and when the page is not yetinitialized, the state of the page is “during initialization”. When thepage is not yet allocated but is already initialized, the state of thepage is “vacant”. The state of the page in which the page is alreadyallocated but not yet initialized is not found in this example. This isbecause, in this example, as will be described later, the page forallocation to the AOU volume is initialized in advance. When the page isalready allocated and is already initialized, the state of the page is“in use”.

The page state change table T21 shows the relationship between thestates of pages. By taking as an example the page during initialization,i.e., any predetermined format pattern such as “000 . . . ” is writtento the page for initialization, when such an initialization process iscompleted, the state of the page is changed to vacant. When the page inthe state of vacant as such is allocated to the AOU volume, the state ofthe page is changed to “in use”. When the page in the state of “in use”is deallocated from the AOU volume, the state of the page is changed to“during initialization”.

FIG. 11 shows a table T22 for management of the pool volumes. Themanagement table T22 manages fields of AOU pool ID, and LDEV-ID of thevolume(s) found in the AOU pool.

FIG. 12 shows a table T23 for management of local copy pairs. The localcopy pair denotes data copying among a plurality of volumes in the samestorage. In the drawing, a primary volume is denoted by PVOL, and a subvolume is denoted by SVOL. A bitmap is denoted by BM.

The management table T23 manages fields of pair ID, primary volumeLDEV-ID, sub volume LDEV-ID, consistency group ID, state of pair, anddifferential bitmap pointer, for example.

The “pair ID” is information for use to identify the local copy pair.The “primary volume LDEV-ID” is information for use to identify theprimary volume. The “sub volume LDEV-ID” is information for use toidentify the sub volume. The “consistency group ID” is information foruse to identify the consistency group for managing, in group, volumeshaving a correlation thereamong. The “state of pair” indicates the stateof local copy pair such as “split” and “resync”. The “differentialbitmap pointer” identifies the differential bitmap for use to manage adifference of storage details between the primary volume and the subvolume. Each of the copy pairs is provided with a differential bitmap.

FIG. 13 shows a table T24 for management of remote copy pairs. Theremote copy pair denotes data copying among a plurality of volumesprovided to each different storages.

The management table T24 manages fields of pair ID, primary volume, subvolume, consistency group ID, state of pair, and differential bitmappointer, for example.

The “pair ID” is information for use to identify the remote copy pair.The “primary volume” indicates information about the primary volume ofthe remote copy pair, and includes sub-fields of “DKC-ID” and “LDEV-ID”.The “DKC-ID” is information for use to identify the storage includingthe primary volume, and “LDEV-ID” is information for use to identify theprimary volume.

The “sub volume” indicates information about the sub volume of theremote copy pair, and similarly to the above, includes sub fields of“DKC-ID” and “LDEV-ID”. The “DKC-ID” is information for use to identifythe storage including the sub volume. The “LDEV-ID” is information foruse to identify the sub volume.

The “consistency group ID” is information for use to identify theconsistency group for managing, in group, the volumes with a correlationthereamong as described above. The “state of pair” indicates the stateof the remote copy pair. The “differential bitmap pointer” isinformation for use to identify the differential bitmap, which manages adifference of storage details between the primary volume and the subvolume. Each of the remote copy pairs is provided with a differentialbitmap.

FIG. 14 shows a table T25 for use to manage the functions of theexternal storage 200, and a table T26 for use to manage the details ofthe functions. In the drawing, the interface is abbreviated to I/F. Thecontents in these tables T25 and T26 are manually set by an operator ofthe storage system, for example. When these tables T25 and T26 can beautomatically created entirely or partially, it is also possible.

The management table T25 manages fields of DKC-ID, and functionalinformation. The “DKC-ID” is information for use to identify theexternal storage 200 in the storage system. The “functional information”is set with a value for use to identify each of the functions of theexternal storage 200.

The management table T26 manages fields of function name, details, andvalue, for example. The “function name” indicates the names of thefunctions of the external storage 200. The names of the functionsinclude “LDEV format”, “shred”, and “AOU”, for example.

The “LDEV format” is the function of initializing the volumes. Thedetails of the LDEV format includes “format pattern”, “format commandI/F”, “entire volume format”, “area-limited format”, and“pattern-limited format”, for example.

The “format pattern” includes patterns of data for use to format thevolumes, e.g., pattern of bit strings of either “0” or “1”, and patternof specific bit strings of such as “0101”. The “format command I/F”indicates whether there is any I/F for accepting a format command comingfrom the main storage 100. When there is such a format command I/F, viathe format command I/F, the main storage 100 can issue a command to theexternal storage 200 for formatting the volume therein. The “entirevolume format” indicates whether the external storage 200 can format thevolume therein in its entirety. The “area-limited format” indicateswhether the external storage 200 can format only any specified area ofthe volume therein. The “pattern-limited format” indicates whether theexternal storage 200 can format the volume therein using the formatpattern designated by the main storage 100, e.g., 0 or 1.

The “shred” is a function of deleting the storage details of the volumeup to the level of no reproduction. The shred includes, in detail,fields of “shred command I/F”, “default shred pattern”, “entire volumeshred”, “area-limited shred”, and “pattern-limited shred”, for example.

The “shred command I/F” indicates whether there is any I/F for acceptinga shred command from the main storage 100. When there is such a shredcommand I/F, the main storage 100 can issue a command for the externalstorage 200 to shred the volume therein via the shred command I/F.

The “default shred pattern” denotes the default shred pattern for theexternal storage to perform a shred process. The shred pattern isrepresented by the writing frequency during shredding and a data stringpattern for each writing, for example. The data string can beexemplified by a data string with bits of 0, a data sting with bits of1, a specific bit string such as “0101”, and a data string in which bitsof 0 and 1 appear at random. An exemplary shred pattern shows thewriting frequency of 3, and the data string for each writing is of “0”,“1”, and “0”.

The “entire volume shred” denotes whether the external storage 200 canshred the volume therein in its entirety. The “area-limited shred”indicates whether or not the external storage 200 can shred only thespecific area of the volume therein. The “pattern-limited shred”indicates whether the external storage 200 can shred the volume thereinusing the shred pattern designated by the main storage 100.

The “AOU” is the function of virtually generating a volume throughdynamic allocation of a page in a pool in accordance with a writeaccess. The details of the AOU includes “AOU function”, “page size”,“area deallocation I/F”, and “pattern-limited area deallocation”.

The “AOU function” denotes whether the external storage 200 is providedwith the function of controlling the AOU volume or not. The “page size”denotes the size of each of the pages configuring the AOU volume. The“area deallocation I/F” denotes whether there is any I/F for acceptingan area deallocation command coming from the main storage 100. Whenthere is such an area deallocation I/F, via the area deallocation I/F,the main storage 100 can issue a command for the external storage 200 todeallocate any page having been allocated to the AOU volume therein. The“pattern-limited area deallocation” denotes, when any area-deallocatedarea is read, whether or not a data pattern, e.g., specific data stringwith “0” and “1”, designated at the time of area deallocation can beused to make a response.

Described now is the operation of the storage system based on FIGS. 15to 30. Note that the flowcharts below show the outline of each of theprocesses, and may be different from any actual computer program.Moreover, those skilled in the art will be able to change, delete, andadd steps in the drawings.

FIG. 15 shows a process for establishing an external connection betweenthe main storage 100 and the external storage 200. This process isexecuted by the first controller 110. The first controller 110 scansports in the storage system, thereby making a search of volumes in thestorage system (S10).

The first controller 110 issues an Inquiry command to each of thus foundvolumes, thereby making an inquiry about the volume type and others(S11). The first controller 110 also issues a “READ Capacity” command,thereby acquiring the size of each of the volumes (S12).

For each of the volumes being the search results, the first controller110 determines the volume type, i.e., physical or AOU (S13). Based onthe response coming from each of the volumes to the Inquiry command, thefirst controller 110 determines the type of the each of the volumes.When determining that any of the volumes is a physical volume, the firstcontroller 110 makes setting of “external physical volume” to the typeof the EDEV 122E and that of the LDEV 123 (S14). The external physicalvolume here means the physical volume in the external storage 200. Whendetermining that the type of the volume is AOU, the first controller 110makes setting of “external AOU volume” to the type of the EDEV 122E andthat of the LDEV 123 (S15). The external AOU volume means the AOU volumein the external storage 200.

The first controller 110 sets, based on the size acquired in S12, thesize of the EDEV 122E and that of the LDEV 123 (S16). The firstcontroller 110 sets the volume state of the LDEV 123 to “formatted” and“no writing” (S17).

FIG. 16 is a flowchart of a process for setting a pool volume. The firstcontroller 110 determines whether a target volume is already set as apool volume or not (S20). When the target volume is already in use as apool volume (S20: YES), the first controller 110 executes an errorprocess (S26). In the error process, an error message is output, forexample.

When the target volume is not in use as a pool volume (S20: NO), thefirst controller 110 then determines whether the target volume iscorrelated to an LU or not (S21). When the target volume is correlatedto an LU (S21: YES), the first controller 110 executes the error process(S26).

When the target volume is not correlated to an LU (S21: NO), the firstcontroller 110 formats the target volume (S22), and sets the type of thetarget volume as “pool volume” (S23). The first controller 110 makessetting of the pool volume management table T22 (S24), and updates thepool management table T17 (S25).

FIG. 17 is a flowchart of a format process. The first controller 110determines whether the target volume is in a state ready for formattingor not (S30). When the target volume is in the state not ready forformatting, e.g., during shredding, (S30: NO), the first controller 110executes the error process (S35), e.g., forwards an error message to anoperator.

When the target volume is in the state ready for formatting (S30: YES),the first controller 110 changes the state of volume to “duringformatting (“during initialization” in the table T21) (S31).

Thereafter, the first controller 110 determines whether the targetvolume is an internal volume or an externally-connected volume (S32).When determining that the volume is the internal volume, the firstcontroller 110 then determines whether the internal volume is a physicalvolume or an AOU volume (S33).

When the internal volume is the physical volume, the first controller110 executes the format process of FIG. 18 to the internal physicalvolume (S40). When the internal volume is the AOU volume, the firstcontroller 110 executes the format process of FIG. 19 to the internalAOU volume (S50).

When determining that the target volume is the externally-connectedvolume (S32), the first controller 110 determines whether the externalvolume connected to the externally-connected volume is a physical volumeor an AOU volume (S34). When the external volume is the physical volume,the first controller 110 executes the format process of FIG. 20 to theexternal physical volume (S60). When the external volume is the AOUvolume, the first controller 110 executes the format process of FIG. 21to the external AOU volume (S70).

FIG. 18 is a flowchart of a process for formatting a physical volumeinside of the storage. The first controller 110 writes any predeterminedformat pattern to the entire internal physical volume being a processingtarget (S41). The first controller 110 then changes the state of format(state of initialization) of the internal physical volumes to “Done”(S42). Moreover, the first controller 110 changes the state of writingto “No” (S43).

FIG. 19 is a flowchart of a format process to be executed to theinternal AOU volume. The first controller 110 deallocates the pagehaving been allocated to the internal AOU volume, and changes the stateof page to “during initialization” (S51).

The first controller 110 also changes the format state of the internalAOU volume to “Done (formatted)” (S52), and changes the state of writingto “no (no writing”) (S53).

The page initialization is performed asynchronous to steps S51 to S53.Among the pages under the management of the AOU pool, the firstcontroller 110 writes the predetermined format pattern to any of thepages having been changed during initialization, i.e., deallocated page(S54). The first controller 110 changes the state of the page writtenwith the format pattern as such from “during initialization” to “vacant”(S55).

FIG. 20 is a flowchart of the format process to be executed to theexternal physical volume. Based on the tables T25 and T26, the firstcontroller 110 determines whether the external storage 200 is providedwith the format command I/F or not (S61).

When the external storage 200 is provided with the format command I/F(S61: YES), the first controller 110 determines whether the formatpattern of the external storage 200 is the same as the predeterminedformat pattern or not. When the determination result is No, the firstcontroller 110 then determines whether the external storage 200 is readyfor pattern-limited format or not (S66). When the format pattern is thesame, or when the external storage 200 is ready for pattern-limitedformat (S66: YES), the first controller 110 issues a command to theexternal storage 200 (the second controller 210) for formatting theexternal physical volume (S62). After the command issued as such, thefirst controller 110 changes the format state to “Done” (S63), andchanges the writing state to “No” (S64) When the external storage 200 isnot provided with the format command I/F (S61: NO), or when the formatpattern is not the same and when the external storage 200 is not readyfor pattern-limited format (S66: NO), the first controller 110 issues awrite command to the external storage 200, and writes the predeterminedformat pattern to the entire external physical volumes being a formattarget (S65).

FIG. 21 is a flowchart of the format process to be executed to theexternal AOU volume. The first controller 110 determines whether theexternal storage 200 is provided with the format command I/F or not(S71). When the external storage 200 is provided with the format commandI/F (S71: YES), the first controller 110 determines whether the formatpattern of the external storage 200 is the same as the predeterminedformat pattern or not. When the determination result is No, the firstcontroller 110 then determines whether the external storage 200 is readyfor pattern-limited format or not (S78). When the format pattern is thesame, or when the external storage 200 is ready for pattern-limitedformat (S78: YES), the first controller 110 issues a command to theexternal storage 200 for formatting the external AOU volume (S72). Afterthe command issued as such, for the external AOU volume, the firstcontroller 110 changes the format state to “Done” (S73), and changes thewriting state to “No” (S74).

On the other hand, when the external storage 200 is not provided withthe format command I/F (S71: NO), or when the format pattern is not thesame, and when the external storage 200 is not ready for pattern-limitedformat (S78: NO), the first controller 110 then determines whether theexternal storage is provided with the area deallocation I/F or not(S75). When the external storage 200 is provided with the areadeallocation I/F (S75: YES), the first controller 110 determines whetherthe format pattern of the external storage is the same as thepredetermined format pattern or not, and when the determination resultis No, the first controller then determines whether the external storage200 is ready for pattern-limited area deallocation or not (S79). Whenthe external storage 200 has the same format pattern or when theexternal storage 200 is ready for pattern-limited area deallocation(S79: YES), the first controller 110 asks the external storage 200 todeallocate the page having been allocated to the external AOU volume(S76). The procedure then goes to steps S73 and S74 in the firstcontroller 110.

When the external storage 200 is not provided with the area deallocationI/F (S75: NO), and when the external storage 200 does not have the sameformat pattern and when the external storage 200 is not ready forpattern-limited area deallocation (S79: NO), the first controller 110issues a write command to the external storage 200, and writes thepredetermined format pattern to the entire external AOU volume being aformat target (S77).

FIG. 22 is a flowchart of the shred process. The shred process is fordeleting data stored in the volumes by writing, into the volumes for apredetermined number of times, a data string of a specific pattern withbits of 0 or 1, or a data string in which bits of 0 and 1 appear atrandom.

The first controller 110 determines whether a target volume is set as apool volume or not (S90). When the target volume is set as a pool volume(S90: YES), the first controller 110 executes the error process (S96).When the target volume is not a pool volume (S90: NO), the firstcontroller 110 determines whether the target volume is in the stateready for shredding or not (S91). When the target volume is in the statenot ready for shredding, e.g., during formatting, (S90: YES), the firstcontroller 110 executes the error process (S96).

When the target volume is in the state ready for shredding (S91: NO),the first controller 110 changes the state of the target volume to“during shredding” (S92), and then determines whether the target volumeis an internal volume or an externally-connected volume (S93).

When determining that the volume is an internal volume, the firstcontroller 110 then determines whether the internal volume is a physicalvolume or an AOU volume (S94). When the internal volume is determined asbeing a physical volume, the shred process of FIG. 23 is executed to theinternal physical volume (S100). When the internal volume is determinedas being an AOU volume, the shred process of FIG. 24 is executed to theinternal AOU volume (S110).

When the target volume is determined as being an externally-connectedvolume (S93), the first controller 110 determines whether the externalvolume correlated to the externally-connected volume is a physicalvolume or an AOU volume (S95). When the external volume is determined asbeing a physical volume, the shred process of FIG. 25 is executed to theexternal physical volume (S120). When the external volume is determinedas being an AOU volume, the shred process of FIG. 26 is executed to theexternal AOU volume (S130).

FIG. 23 is a flowchart of the shred process to be executed to theinternal physical volume. The first controller 110 writes thepredetermined shred pattern to the entire internal physical volume(S101), and changes the shred state of the internal physical volume to“Done (shredded)” (S102).

FIG. 24 is a flowchart of the shred process to be executed to theinternal AOU volume. The first controller 110 writes the predeterminedshred pattern to each of the pages allocated to the internal AOU volume(S111).

The first controller 110 determines whether the last shred pattern isthe same as the format pattern or not (S112). The last shred pattern isany one of the shred patterns to be written into the volume for aplurality of times, i.e., pattern of a data string to be lastly writteninto the volume. When the last shred pattern to be written into theinternal AOU volume is the same as the format pattern of the internalAOU volume (S112: YES), there is no need to format the pages having beenallocated to the internal AOU volume. Therefore, the first controller110 deallocates the pages having been allocated to the internal AOUvolume, and changes the page state thereof to “vacant” (S113). The firstcontroller 110 then changes the shred state of the internal AOU volumeto “Done” (S114).

FIG. 25 is a flowchart of the shred process to be executed to theexternal physical volume. The first controller 110 determines whetherthe external storage 200 is provided with the shred command I/F or not(S121).

When the external storage 200 is provided with the shred command I/F(S121: YES), the first controller 110 determines whether the shredpattern of the external storage 200 is the same as the predeterminedshred pattern or not. When the determination result is No, the firstcontroller 110 then determines whether the external storage 200 is readyfor pattern-limited shred or not (S125). When the shred pattern is thesame, or when the external storage 200 is ready for pattern-limitedshred (S125: YES), the first controller 110 issues a command to theexternal storage 200 for executing the shred process to the externalphysical volume (S124).

When the external storage 200 is not provided with the shred command I/F(S121: NO), or when the shred pattern is not the same, and when theexternal storage 200 is not ready for pattern-limited shred (S125: NO),the first controller 110 issues a write command to the external storage200, and writes the predetermined shred pattern to the entire externalphysical volume for a predetermined number of times (S122). The firstcontroller 110 then changes the shred state of the external physicalvolume to “Done” (S123).

FIG. 26 is a flowchart of the shred process to be executed to theexternal AOU volume. The first controller 110 determines whether theexternal storage 200 is provided with the shred command I/F or not(S131). When the external storage 200 is provided with the shred commandI/F (S131: YES), the first controller 110 then determines whether theshred pattern of the external storage 200 is the same as thepredetermined shred pattern or not. When the determination result is No,the first controller 110 then determines whether the external storage200 is ready for pattern-limited shred or not (S133). When the shredpattern is the same, or when the external storage 200 is ready forpattern-limited shred (S133: YES), the first controller 110 issues acommand to the external storage 200 for executing the shred process tothe external AOU volume (S137). The first controller 110 then changesthe shred state of the external AOU volume to “Done” (S136).

On the other hand, when the external storage 200 is not provided withthe shred command I/F (S131: NO), the first controller 110 issues awrite command to the external storage 200, and writes the predeterminedshred pattern to the entire external AOU volume for a predeterminednumber of times (S132).

The first controller 110 then determines whether the external storage200 is provided with the format command I/F or not (S134).

When the external storage 200 is provided with the format command I/F(S134: YES), the first controller 110 determines whether the formatpattern of the external storage 200 is the same as the last shredpattern or not. When the determination result is No, the firstcontroller 110 then determines whether the external storage 200 is readyfor pattern-limited format or not (S140). When the format pattern is thesame, or when the external storage 200 is ready for pattern-limitedformat (S140: YES), the first controller 110 issues a command to theexternal storage 200 for executing the format process to the externalAOU volume (S135). The first controller 110 then changes the shred stateof the external AOU volume to “Done” (S136), and this is the end of theprocess.

When the external storage 200 is not provided with the format commandI/F (S134: NO), and when the format pattern is not the same as the lastshred pattern, and when the external storage 200 is not ready forpattern-limited format (S140: NO), the first controller 110 determineswhether the external storage 200 is provided with the area deallocationI/F or not (S138). When the external storage 200 is not provided withthe area deallocation I/F (S138: NO), the first controller 110determines whether the format pattern of the external storage 200 is thesame as the last shred pattern or not, and when the determination resultis No, the first controller 110 then determines whether the externalstorage 200 is ready for pattern-limited area deallocation or not(S141). When the format pattern is the same as the last shred pattern orwhen the external storage 200 is ready for pattern-limited areadeallocation (S141: YES), the first controller 110 changes the shredstate of the external AOU volume to “Done” (S136), and this is the endof the process.

When the external storage 200 is provided with the area deallocation I/F(S138: YES), and when the format pattern is not the same as the lastshred pattern and when external storage 200 is not ready forpattern-limited area deallocation (S141: NO), the first controller 110asks the external storage 200 to deallocate the pages having beenallocated to the external AOU volume (S139). The first controller 110then changes the shred state of the external AOU volume to “Done”(S136), and this is the end of the process.

FIG. 27 is a flowchart of a write process for writing data to the datavolume. First of all, for the data volume being a write target, thefirst controller 110 sets the volume state in the LDEV management tableT10 to “Yes (data written)” (S150).

The first controller 110 then determines whether a copy pair is formedfor the data volume being a write target, and the data volume is duringdifferential management or not (S151) When the data volume is duringcopy pair formation and differential management (S151: YES), the firstcontroller 110 updates the bitmap for differential management use(S152). When the data volume being a write target is not during copypair formation, or when such a data volume is during copy pair formationbut not during differential management (S151: NO), the procedure skipsstep S152.

The first controller 110 then determines whether the data volume being awrite target is an internal volume or an externally-connected volume(S153). When the write-target data volume is an internal volume, thefirst controller 110 determines whether the write-target data volume isa physical volume or an AOU volume (S154).

When the write-target data volume is an AOU volume, the first controller110 determines whether a write-target area in the write-target datavolume is allocated with a page or not (S155).

When the write-target area is not yet allocated with a page (S155: NO),the first controller 110 selects any vacant page from the pool, andallocates the page to the write-target area of the write-target datavolume (S156). That is, for any new writing, the page allocation isperformed first. On the other hand, when the write-target area isalready allocated with a page (S155: YES), the procedure skips stepS156.

The first controller 110 receives the write data from the host 10(S157), and stores the data into the cache memory 113. The firstcontroller 110 then determines whether the write-target area is locatedin the main storage 100 or in the external storage 200 (S158). As forthe write-target area, when the write-target data volume (LDEV 123A) isan internal physical volume or an external volume, the write-target areais the VDEV 122V or the EDEV 122E correlated to the LDEV 123A. When thewrite-target data volume (LDEV 123) is an internal AOU volume, thewrite-target area is the VDEV 122V or the EDEV 122E of the pool volume123P correlated to any allocated pool page. When the write-target datavolume 123A is an internal AOU volume, the process varies depending onwhether the pool volume 123P for the correlated page is an internalvolume or an external volume.

When the write-target area is located inside of the main storage 100,the first controller 110 writes the write data to the PDEV 121corresponding to the write-target area from the cache memory 113(destaging), and notifies the host 10 of completion of writing (S159).When the write-target area is located inside of the external storage200, the first controller 110 transfers the write data to the externalstorage 200 for writing it into the external volume (S160).

On the other hand, when the write-target data volume is a physicalvolume in the main storage 100 (S154), the first controller 110 receivesthe write data from the host 10 (S161), and destages the write data(S162).

When the write-target data volume is an externally-connected volume(S153), the first controller 110 receives the write data from the host10 (S163), and transfers the write data to the external storage 200 forwriting it into the external volume (S164).

When the first controller 110 is provided with the cache memory 113 asin this example, after storing the write data provided from the host 10into the cache memory 113, the first controller 110 can notify the host10 of processing completion of write command. Thereafter, at anyappropriate timing, the first controller 110 can perform destaging orwriting to the external storage 200. As such, the write command providedfrom the host 10 can be processed asynchronously to destaging or datawriting to the external storage 200. Alternatively, after completingdestaging or data writing to the external storage 200, the firstcontroller 110 may notify the host 10 of processing completion of writecommand. Such a process is referred to as synchronous process.

FIG. 28 is a flowchart of a pair formation copy process. The pairformation copy process is for completing initial copying between volumesof a copy pair, i.e., primary and sub volumes, for creating a copy (subvolume) of a volume (primary volume). The first controller 110 sets“Yes” to the writing state of the sub volume (S170), and determineswhether the primary volume is a physical volume or an AOU volume (S171).

When the primary volume is a physical volume, the first controller 110copies the primary volume in its entirety into the sub volume (S172).The first controller 110 then determines whether the write-target areato the sub volume, i.e., copy-target area, is located in the mainstorage 100 or in the external storage 200 (S173).

When the write-target area is located inside of the main storage 100,the first controller 110 performs destaging (S174) When the write-targetarea is located inside of the external storage 200, the first controller110 transfers the copy data, i.e., data of the primary volume, to theexternal storage 200 for writing thereinto (S175).

When the primary volume is an AOU volume (S171), the first controller110 determines whether the sub volume is a physical volume or an AOUvolume (S176). When the sub volume is a physical volume, the firstcontroller 110 writes any predetermined format pattern to an area of thesub volume (S177) The area is the one corresponding to the area in theprimary volume (AOU volume) not yet allocated with a page. That is, toany area not yet written with data in the primary volume, thecorresponding area in the sub volume is written with “0”, i.e., when theformat pattern is 0.

The first controller 110 then copies the data of the area in the primaryvolume allocated with a page to the sub volume (S178), and the proceduregoes to step S173.

When the sub volume is an AOU volume (S176), the first controller 110determines whether the sub volume is an internal volume or anexternally-connected volume (S179). When the sub volume is an internalvolume, i.e., an internal AOU volume, the first controller 110deallocates the page allocated to the sub volume (AOU volume)corresponding to the area not yet allocated with a page in the primaryvolume (AOU volume) (S180). That is, for the area not yet written withdata in the primary volume, the first controller 110 puts, back to thepool, the page allocated to the corresponding area in the sub volume.Thereafter, the procedure goes to step S178 in the first controller 110.

When the sub volume is an externally-connected volume (S179), the firstcontroller 110 determines whether the external storage corresponding tothe externally-connected volume is provided with either the areadeallocation I/F or the format command I/F, and whether the formatpattern is the same as the predetermined format pattern or not. When thepattern is not the same, the first controller 110 then determineswhether the external storage 200 is ready for pattern-limited formattingor pattern-limited area deallocation or not (S181).

When the external storage 200 is provided with either the areadeallocation I/F or the format command I/F, when the format pattern isthe same as the predetermined format pattern, and if the pattern is notthe same, when the external storage 200 is ready for pattern-limitedformatting or pattern-limited area deallocation (S181: YES), the firstcontroller 110 issues a command to the external storage 200 for eitherarea deallocation or formatting (S182), and the procedure goes to stepS178. Also in this example, destaging or copying to the external storage200 is possible asynchronously to the pair formation copy utilizing thecache memory 113. The below is also the same whether the process is tobe executed synchronously or asynchronously, thereby no specificdescription will be given again.

FIG. 29 is a flowchart of a pair resync copy process. The pair resynccopying is a process for copying, from a primary volume to a sub volume,a difference between the volumes for establishing synchronizationbetween the storage details in a volume pair, i.e., primary and subvolumes. The difference between the volumes is managed by a bitmap fordifferential management use (differential bitmap). When there is anydifference between the primary and sub volumes, the area of thedifferential bitmap corresponding to the area of the difference is setto ON.

The first controller 110 determines whether the primary volume is aphysical volume or an AOU volume (S191). When the primary volume is aphysical volume, the first controller 110 performs data copying from theprimary volume to the sub volume for the ON-area in the differentialbitmap (S192).

The first controller 110 then determines whether the write-target areain the sub volume, i.e., copy-destination target area, is located in theinternal volume or in the external volume (S193). When thecopy-destination target area is located in the internal volume, thefirst controller 110 performs destaging (S194). When thecopy-destination target area is located in the external volume, thefirst controller 110 transfers the copy data to the external storage 200for writing thereinto (S195).

When the primary volume is an AOU volume (S191), the first controller110 determines whether the sub volume is a physical volume or an AOUvolume (S196). When the sub volume is a physical volume, the firstcontroller 110 writes the predetermined format pattern into the subvolume for an area where the differential bitmap is turned ON and anarea of the primary volume where no page is allocated, i.e., area of theprimary volume through with page deallocation after data synchronizationbetween the volumes (S197). Such an area is hereinafter referred to aspredetermined area. The procedure then goes to step S192.

When the sub volume is an AOU volume (S196), the first controller 110determines whether the sub volume is an internal volume or anexternally-connected volume (S198). When the sub volume is an internalvolume, the first controller 110 deallocates the page having beenallocated to the sub volume for the predetermined area (S199).

When the sub volume is an externally-connected volume, the firstcontroller 110 determines whether the external storage 200 is providedwith the area deallocation I/F or not. When determining that theexternal storage 200 is provided with the area deallocation I/F, thefirst controller 110 then determines whether the format pattern of theexternal storage 200 is the same as the predetermined format pattern ornot, and when the pattern is not the same, the first controller 110determines whether the external storage 200 is ready for pattern-limitedarea deallocation or not (S200). When the external storage 200 isprovided with the area deallocation I/F, and when the format pattern isthe same as the predetermined format pattern, and even if the pattern isnot the same, when the external storage 200 is ready for pattern-limitedformatting or pattern-limited area deallocation (S200: YES), the firstcontroller 110 asks the external storage 200 to deallocate the pagehaving been allocated to the sub volume (S201). The area deallocationcommand includes information for volume identification, e.g., LUN, andan area range in the volume for deallocation, e.g., head LBA and size.The external storage 200 deallocates all of the pages found in the arearange asked for deallocation in the AOU pages under the management ofthe external storage 200. As for any page managed by the externalstorage 200 including partially the area asked for deallocation, thepage is not deallocated but only the area asked for deallocation thereinis filled with any predetermined format data. This is because the areaof the page not asked for deallocation may include any effective data.The procedure then goes to step S192 in the first controller 110. On theother hand, when the external storage 200 is not provided with the areadeallocation I/F (S200: NO), the procedure goes to step S192 in thefirst controller 110.

FIG. 30 is a flowchart of a pair restore copy process. The pair restorecopy process is a process for copying, from a sub volume to a primaryvolume, a difference of storage details between these volumes forrestoring the storage details of the primary volume.

The first controller 110 determines whether the sub volume is a physicalvolume or an AOU volume (S211). When the sub volume is a physicalvolume, the first controller 110 copies data from the sub volume to theprimary volume for an-ON area in the differential bitmap (S212).

The first controller 110 then determines whether the write-target areain the primary volume, i.e., copy-destination target area, is located inthe internal volume or in the external volume (S213). When thecopy-destination target area is located in the internal volume, thefirst controller 110 performs destaging (S214). When thecopy-destination target area is located in the external volume, thefirst controller 110 transfers the copy data to the external storage 200for writing thereinto (S215).

When the sub volume being a copy source is an AOU volume (S211), thefirst controller 110 determines whether the sub volume is an internalvolume or an externally-connected volume (S216). When the sub volume isan external AOU volume, the procedure goes to step S212.

When the sub volume is an internal AOU volume, the first controller 110determines whether the primary volume being a copy destination is aphysical volume or an AOU volume (S217) When the primary volume is aphysical volume, the first controller 110 writes the predeterminedformat pattern to the primary volume, i.e., to an area where thedifferential bitmap is ON, and an area where a page is not yet allocatedto the sub volume (S218). Such an area is hereinafter referred to aspredetermined area.

When the primary volume is an AOU volume (S217), the first controller110 determines whether the primary volume is an internal volume or anexternally-connected volume (S218) When the primary volume is aninternal AOU volume, the first controller 110 deallocates, in thepredetermined area, any page having been allocated to the primary volume(S220). The procedure then goes to step S212.

When the primary volume is an external AOU volume, the first controller110 determines whether the external storage 200 is provided with thearea deallocation I/F or not. When determining that the external storage200 is provided with the area deallocation I/F, the first controller 110then determines whether the format pattern of the external storage 200is the same as the predetermined format pattern or not, and when thepattern is not the same, the first controller 110 determines whether theexternal storage 200 is ready for pattern-limited area deallocation ornot (S221). When the external storage 200 is provided with the areadeallocation I/F, and when the format pattern is the same as thepredetermined format pattern, and even if the pattern is not the same,when the external storage 200 is ready for pattern-limited formatting orpattern-limited area deallocation (S221: YES), the first controller 110asks the external storage 200 to deallocate the predetermined area(S222). The procedure then goes to step S212. The process for theexternal storage 200 provided with such an area deallocation command isthe same as the pair resync copy process, and thus is not describedtwice. When the external storage 200 is not provided with the areadeallocation I/F (S221: NO), the procedure goes to step S212.

As described in detail above, in this example, the externally-connectedvolume in the main storage 100 is correlated to the external AOU volumein the external storage 200 so that the storage resources in the storagesystem can be used with good efficiency.

Moreover, in this example, at the time of command issuing, i.e., formatcommand, shred command, pair formation copy command, pair resynccommand, and pair restore command, the commands are converted beforebeing directed to the external storage 200 for reducing the frequency ofa write access to the external volume as much as possible.

For example, when the external storage 200 is provided with the formatcommand I/F and/or the area deallocation I/F, by issuing a command forutilizing these I/F, the need for a write process to the external volumein its entirety can be prevented from occurring. As a result, when theexternal volume is an AOU volume, any unnecessary page can be preventedfrom being allocated thereto, thereby being able to utilize a page withgood efficiency.

Second Example

Based on FIGS. 31 to 45, described now is a second example of theinvention. The following examples including the second example aremodified examples of the first example described above. Accordingly, inthe following examples, any difference from the first example isdescribed mainly. In this second example, the first controller 110 takescharge of managing update related to internal volumes and update relatedto external volumes.

FIG. 31 is a diagram for illustrating the main components in a storagesystem of this example. First controller 110 is provided with an updatemanagement table T30A for update management of the internal volumes, andan update management table T30B for update management of the externalvolumes. In the below, when no discrimination is required between thesetables, these tables are referred to as update management tables T30.

FIG. 32 shows the update management table T30 for use to manage fieldsof update management size and update information, for example. The“update management size” is a unit for update management of a volume.The update management size is preferably set the same as the page size.This is surely not restrictive, and any size different from the pagesize may be used for update management. The “update information” is thefield of managing the state of every update management area.

The details of the update information are shown in the table T31. Thetables T30 and T31 are each equivalent to the update bitmap for use tomanage any updated area. The table T31 includes fields of updatemanagement area ID, state of writing, and state of format. The “updatemanagement area ID” is information for use to identify the areas forupdate management. When the update management size and the page size arethe same, for example, the pages in total configuring each of thevolumes share the same update management area.

The “state of writing” indicates whether the update management area hasbeen written with data or not. The “state of format” indicates whetherthe update management area has been formatted or not.

FIG. 33 shows the VDEV/EDEV management table T32 in this example. Thedifference from the table T13 of FIG. 8 lies in that, as shown at theright end thereof, the field of “format pattern” is additionallyprovided. The “format pattern” is the field of managing the formatpatterns of the VDEVs and EDEVs.

FIG. 34 is a flowchart of an external connection setting process in thisexample. Unlike the flowchart of FIG. 15, the first controller 110issues an Inquiry command, thereby making an inquiry to the volumesabout the volume type, the page size, and the format pattern (S11A).That is, the Inquiry command in this example is expanded compared withthat in the first example. When the volume is an AOU volume (S13), thefirst controller 110 enters the page size and format pattern acquired instep S11 into the table T32 (S18).

FIG. 35 is a flowchart of a write process to the externally-connectedvolume in this example. Upon reception of the write data from the host10, the first controller 110 stores the write data into the cache memory113 (S300).

By referring to the update management table T30B, the first controller110 determines whether any updated area is to be overwritten or not(S301). When the area is to be overwritten (S301: YES), the firstcontroller 110 issues a write command to the external storage 200, andwrites the write data into the external volume (S302).

On the other hand, when the area is not to be overwritten (S301: NO),i.e., when the area is updated for the first time, the first controller110 changes, to “Yes”, the writing state of the update-target area inthe update information table T31 (S303).

The first controller 110 also determines whether the write-target area,i.e., update-target area, has been formatted or not based on the tableT31 (S304). When the write-target area has been formatted (S304: YES),the procedure goes to step S302. When the write-target area has not yetbeen formatted (S304: NO), the first controller 110 fills, with theformat pattern, the area of the update management size not written withthe write data, and changes the format state of the update-target areato “formatted”. The procedure then goes to step S302. Note here that,alternatively, the update information T31 may be used only for managingthe writing state but not the format state. If this is the case,formatting is performed in response to writing so that the area showing“No” for the writing state is always in the state of not-yet formatted.In FIG. 35, the difference lies in that the procedure skips step S304,i.e., the format state always shows “Not yet”, and the process forchanging the format state in step S305 is eliminated. With the updateinformation T31 managing the format state separately from the writingstate, the format process can be performed asynchronously to the writeprocess, i.e., format process before and separately from the writeprocess. The asynchronous format process will be described later.

FIG. 36 schematically shows the process for step S305. In the updatemanagement size, write data is stored at a predetermined position. Tothe vacant area observed before and after the write data, a formatpattern under the management of the table T32 is written. That is, inthis example, the format process by the external storage 200 is nottrusted, and data is created in the main storage 100 in a unit of updatemanagement size.

FIG. 37 shows a process for reading data from the externally-connectedvolume. By referring to the tables T30B and T31, the first controller110 determines whether a read-target area has been already updated ornot (S310).

When the read-target area has been updated (S310: YES), the firstcontroller 110 issues a read command to the external storage 200, andreads the data from the external volume. Thus read data is thenforwarded to the host 10 (S311).

When the read-target area is not yet updated (S310: NO), the firstcontroller 110 forwards, to the host 10, the format pattern correlatedto the externally-connected volume without accessing the externalvolume, i.e., without issuing a read command to the external storage(S312).

FIG. 38 shows a format process to be executed to the external AOUvolume. The difference from the flowchart of FIG. 21 lies in that thefirst controller 110 changes, lastly, the writing state in the table T31to “No” entirely for the externally-connected volume connected to theexternal AOU volume (S320).

FIG. 39 shows a process for asynchronously formatting the externalphysical volume. The first controller 110 sets a format pattern to eachof the update management areas of the external physical volume, i.e.,area of the update management size (S330). The first controller 110forwards the data storing the format pattern to the external storage200, and writes the data into the external physical volume (S331).

FIG. 40 is a flowchart of a write process to be executed to the internalphysical volume. The difference from the flowchart of FIG. 35 lies inthat destaging is performed as an alternative to write data transferringto the external storage 200 (S320 of FIG. 35) (S340). Similarly to thewrite process of FIG. 35 to the external volume, when the updateinformation T is not used to manage the format state, the procedureskips step S304 (the format state always shows “Not yet”, and theprocess in step S305 for changing the format state is eliminated.

FIG. 41 shows a process for reading data from the internal physicalvolume. The difference from the flowchart of FIG. 37 lies in that theread-target data is staged as alternative to data reading from theexternal volume (S311 of FIG. 37), and the result is forwarded to thehost 10 (S350). That is, data is read from the PDEV 121 corresponding tothe internal physical volume for storage into the cache memory 113, andforwards the data stored in the cache memory 113 back to the host 10.

FIG. 42 is a flowchart of a format process to be executed to theinternal physical volume. The difference from the flowchart of FIG. 18lies in that the first controller 110 changes, lastly, to “No”, thewriting state in the update information table T31 entirely for theinternal physical volume (S360).

FIG. 43 is a flowchart showing how the internal physical volumes aresubjected to the format process in an asynchronous manner. Thedifference from the flowchart of FIG. 39 lies in that the updatemanagement area data set with the format pattern is not written bytransferring to the external storage 200 (S331 of FIG. 39) but bydestaging (S331A).

FIG. 44 is a flowchart of a pair formation copy process. The resync copyprocess is similar to the formation copy process, and thus onlydifferences from the formation copy process are described. Moreover, therestore copy process is equivalent to the process in which primary andsub volumes are inverted from those in the resync copy process asdescribed in the first example, and thus is not described twice. Thefirst controller 110 sets, in the LDEV management table T10, the writingstate of the sub volume to “Yes” (S370). The first controller 110 alsosets, in the update information table T31 for all of the sub volumes,the writing state to “No”, and the format state to “Not yet” (S371).Note that, in the resync copy process, for any area in the primaryvolume not written with data, the writing state of the updateinformation of the sub volume is set to “No”, and the format state to“Not yet”.

The first controller 110 determines whether the primary volume is aphysical volume or an AOU volume (S372). When the primary volume is anAOU volume, the steps of S176 to S182 of FIG. 28 are executed asappropriate (S373). For the area written with data in the primaryvolume, the first controller 110 changes, to “Yes (data written)”, thewriting state of the sub volume in the update information table T31(S374). Thereafter, via a coupler 4, the procedure goes to step S383that will be described later (FIG. 45).

When the primary volume is a physical volume, the first controller 110determines whether the sub volume is a physical volume or an AOU volume(S375). When the sub volume is a physical volume, the procedure goes tostep S383 that will be described later (FIG. 45). Note that,alternatively, when the sub volume is an external physical volume, thefirst controller 110 may write a format pattern to the sub volume forthe area in the primary volume not yet written with data. By writing theformat pattern as such, even if an external volume is accessed withoutvia the main storage 100, any predetermined format pattern can be read.

When the sub volume is an AOU volume, the first controller 110determines whether the sub volume is an internal volume or anexternally-connected volume (S377). When the sub volume is an internalAOU volume, the first controller 110 deallocates the page allocated tothe sub volume for the area in the primary volume not written with data(S378).

When the sub volume is an externally-connected volume, the firstcontroller 110 determines whether the external storage 200 is providedwith the format command I/F or the area deallocation I/F. When theexternal storage 200 is provided with the format I/F or the areadeallocation I/F, the first controller 110 then determines whether theformat pattern of the external storage 200 is the same as thepredetermined format pattern or not. When the determination result isNO, the first controller 110 determines whether the external storage 200is ready for pattern-limited formatting area deallocation (S379) or not.When the external storage 200 is provided with the format command I/F orthe area deallocation I/F, and when the format pattern is the same asthe predetermined format pattern, and even if the pattern is not thesame, when the external storage 200 is ready for pattern-limitedformatting pattern-limited area deallocation (S379: YES), the firstcontroller 110 issues a command to the external storage 200 forformatting or area deallocation (S380). When the external storage 200 isnot provided with the area deallocation I/F (S379: NO), the proceduregoes to step S376. Herein, in the resync copy process, for the area inthe primary volume not yet written with data, an area deallocationcommand is issued to the external storage 200 of the sub volume.

FIG. 45 is a flowchart continued from the flowchart of FIG. 44. Thefirst controller 110 changes, for the area in the primary volume writtenwith data, the writing state of the sub volume in the update informationtable T31 to “Yes” (S381). The first controller 110 copies the data inthe primary volume into the sub volume for the area in the primaryvolume written with data, and changes, to “Done”, the format state ofthe sub volume in the update information table T31 (S382). In the resynccopy process, for the areas in the primary volume showing “Yes” forwriting, for the ON-area in the differential bitmap, data copying to thesub volume is performed, and the update information table T31 is updatedfor the sub volume. Herein, when the management unit of the differentialbitmap is larger than that of the update information, i.e., updatebitmap, and when the differential bitmap includes any area showing “No”for data writing from the primary volume in the ON-area, only any areashowing “Yes” for writing in the ON-area of the differential bitmap maybe subjected to copying to the sub volume, and updating of the updateinformation.

The first controller 110 determines whether the area of the sub volumefor data writing, i.e., copy-destination target area, is located in theinternal volume or in the external volume (S383). When thecopy-destination target area is located in the internal volume, thefirst controller 110 performs destaging (S384). When thecopy-destination target area is located in the external volume, thefirst controller 110 forwards the copy data to the external storage 200,and writes the copy data to the external volume (S385).

The second example configured as such shows the effects similar to thosein the first example. Moreover, in this example, even if the primaryvolume being a volume copy pair, i.e., sub volume in restore, is aphysical volume, in the copy process to the sub volume, i.e., copyprocess to the primary volume in restore, any unnecessary page can beprevented from being allocated to the sub volume so that the page can beutilized with good efficiency. Moreover, in this example, the formatpattern is used to fill around the write data on an update managementsize basis, and the write data is written to the external volume. Assuch, irrespective of whether the external storage 200 is executing theformat process to the external volume or not, the data can be normallystored into the external volume. That is, in this example, even if theexternal storage 200 cannot execute the format process with the patternsimilar to that in the main storage 100, the format process similar tothat of the main storage 100 can be executed to the external volume.Moreover, in this example, the format pattern is not written at the timepoint when the format command comes, but in response to writing from thehost, and the portion in the update management area not written with thewrite data is filled with the format pattern, thereby increasing thespeed of the completion response at the time of format command issuing.

In this example, for any area not yet written with data in the volumeconnected to the external volume, i.e., externally-connected volume,when a request comes from the host 10 for data reading, the formatpattern can be responded without accessing the external volume. As such,even when the response pattern related to the data not-yet-written areais not the same in the main storage 100 and the external storage 200,the response similar to that of the main storage 100 can be put back tothe host 10.

Third Example

Based on FIG. 46, a third example is described. In this example, inresponse to a command coming from the management server 20, the LDEVmanagement table T10 is set with information. FIG. 46 is a flowchart ofa process for establishing an external connection between the mainstorage 100 and the external storage 200 in this example.

The first controller 110 scans ports in the storage system, therebymaking a search of volumes in the storage system (S390). The firstcontroller 110 issues an Inquiry command to each of thus found volumes,thereby making an inquiry about the volume type and others (S391). Thefirst controller 110 also issues a “READ Capacity” command, therebyacquiring the size of each of the volumes (S392).

The first controller 110 forwards information collected from the volumesto the management server 20 (S392). An operator of the storage systemdesignates the type of the external volume and the volume for mappingvia the management server 20.

Upon reception of the type of the external volume and the command aboutthe mapping destination from the management server 20 (S394), the firstcontroller 110 determines whether the volume type is physical or AOU foreach of the volumes (S395).

When the volume type is physical, the first controller 110 sets, as“external physical volume”, the type of the EDEV 122E and that of theLDEV 123 (S396). When the volume type is AOU, the first controller 110sets, as “external AOU volume”, the type of the EDEV 122E and that ofthe LDEV 123 (S397). Based on the size acquired in step S392, the firstcontroller 110 sets the size of the EDEV 122E and the size of the LDEV123 (S398).

The third example configured as such has the effects similar to those ofthe first example.

Fourth Example

Based on FIGS. 47 to 53, a fourth example is described. In this example,a determination is made in advance about whether data for writing intovolumes has the format pattern same as the predetermined format pattern.If with write data showing correspondence to the format pattern, pagedeallocation is performed without actually writing the data.

FIG. 47 shows a process for writing write data to the data volume. Thedifference from the flowchart of FIG. 27 lies in that, after receivingthe write data from the host 10 (S157), the first controller 110determines whether any new page is required to be allocated or not forwriting the data to the internal AOU volume (S500).

When allocation of a new page is required (S500: YES), the firstcontroller 110 determines whether the write data has the format patternsame as the predetermined format pattern (S501). When the write data isthe same as the predetermined format pattern (S501: YES), the firstcontroller 110 deallocates the new page having been allocated in stepS500 (S502). The procedure then goes to step S158. When this example isapplied to the second example, also for the external AOU volume, pagedeallocation can be performed without actually writing the write datashowing the correspondence to the format pattern. In the updateinformation in the second example, when the host writing to the areashowing the writing state of “No” in the update information for thevolume shows the correspondence to the format pattern, the attribute ofthe write data stored in the cache memory in the first controller 110 ischanged from dirty to clean, and the writing state thereof is remained“No”. Herein, the dirty state means the state in which destaging or datatransfer to the external storage is not completed. The clean state meansthe state in which destaging or data transfer to the external storage iscompleted. By changing, to clean state, the attribute of the data storedin the cache memory in the first controller 110 before data transferinto the external storage 200, the data is prevented from beingtransferred to the external storage 200, thereby being able to preventany page for storage from being allocated to the external storage.

Herein, when allocation of any new page is not required (S500: NO), theprocedure skips steps S501 and S502, and moves to step S158. When thewrite data shows no correspondence to the format pattern (S501: NO), theprocedure skips S502, and moves to S158.

FIG. 48 is a flowchart of a process for deallocating any page of theinternal AOU volume asynchronously to a command from the host 10. Thefirst controller 110 reads data from the area of the internal AOU volumeallocated with a page (S510), and determines whether thus read data hasthe correspondence to the predetermined format pattern or not (S511).

When the data read from the internal AOU volume has the correspondenceto the format pattern (S511: YES), the first controller 110 deallocatesany page storing the data same as the format pattern from the internalAOU volume (S512). When the data read from the internal AOU volume doesnot have the correspondence to the format pattern (S511: NO), theprocedure skips S512, and this is the end of the process.

FIG. 49 is a flowchart of a process for deallocating any page of theexternal AOU volume asynchronously to a command from the host 10. Byreferring to the tables T25 and T26 of FIG. 14, the first controller 110determines whether the external storage 200 including the external AOUvolume is provided with the area deallocation I/F or not. When the areadeallocation I/F is provided, the first controller 110 then determineswhether the format pattern of the external storage 200 is the same asthe predetermined format pattern or not. When the determination resultis No, the first controller 110 determines whether the external storage200 is ready for pattern-limited area deallocation or not (S520).

When the external storage 200 is provided with the area deallocationI/F, and when the format pattern is the same as the predetermined formatpattern, or even when the format pattern is not the same, when theexternal storage 200 is ready for pattern-limited area deallocation(S520: YES), the first controller 110 reads data from the area of theexternal AOU volume allocated with the page (S521), and determineswhether thus read data has the correspondence to the format pattern ornot (S522).

When the read data has the correspondence to the format pattern (S522:YES), the first controller 110 issues a command to the external storage200 for deallocating the page storing the data having the correspondenceto the format pattern (S523) Herein, as for any page managed by theexternal storage 200 including partially the area asked fordeallocation, the page is not deallocated but only the area asked fordeallocation therein is filled with any predetermined format data. Thisis because the area of the page not asked for deallocation may includeany effective data. It is preferable to perform the data comparisonprocess and the deallocation command process on the basis of the pagemanaged by the external storage, or on the basis of multiples of thepage size.

When the external storage 200 is not provided with the area deallocationI/F, when the format pattern is not the same and when the externalstorage 200 is not ready for pattern-limited area deallocation (S520:NO), and when the data read from the external AOU volume does not havethe correspondence to the format pattern (S522: NO), this is the end ofthe process. Described above is the case where the page deallocationprocess to the external AOU volume and the data comparison process areexecuted mainly by the main storage 100 asynchronously to a command fromthe host. However, when the external storage 200 has the function ofasynchronous data comparison and page deallocation for the AOU volume,the external storage 200 may mainly perform the deallocation process. Ifthis is the case, the external storage 200 may execute the process inresponse to a command coming from the main storage 100 and themanagement server, or the external storage 200 may execute the processautomatically.

FIG. 50 is a flowchart of a pair formation copy process. The differencefrom the flowchart of FIG. 28 lies in that the data comparison processis executed after data copying from a primary volume to a sub volume(S172 or S178) (S550). Also in the resync copy process and the restorecopy process, after data copying, the data comparison process isexecuted in accordance with the types of volumes and the functions ofthe external storage 200, and then the area deallocation process isexecuted. Therefore, no description is given here again.

FIG. 51 shows the details of the data comparison process (S550) of FIG.50. The first controller 110 determines whether the sub volume is aphysical volume or an AOU volume (S551). When the sub volume isdetermined as being a physical volume, the procedure returns to theflowchart of FIG. 50.

When the sub volume is determined as being an AOU volume, the firstcontroller 110 determines whether the sub volume is an internal volumeor an externally-connected volume (S552).

When the sub volume is an internal volume, that is, when the sub volumeis an internal AOU volume, the first controller 110 determines whetherthe copy data copied from the primary volume to the sub volume has thecorrespondence to the predetermined format pattern (S553).

When the copy data has the correspondence to the format pattern (S553:YES), the first controller 110 deallocates the page having beenallocated to the sub volume, i.e., internal AOU volume, for storage ofcopy data (S554). Note that, when the copy data is not thenewly-allocated page, and when the page is only a part, there may be acase that the page includes any effective data, and thus the page is notdeallocated. When the copy data does not have the correspondence to theformat pattern, the procedure returns to the flowchart of S52.

When the sub volume is an externally-connected volume, the firstcontroller 110 determines whether the external storage 200 is providedwith the area deallocation I/F or not, and whether the format pattern ofthe external storage 200 is the same as the predetermined format patternor not. When the format pattern is not the same, the first controller110 determines whether the external storage 200 is ready forpattern-limited area deallocation or not (S555). When the externalstorage 200 is provided with the area deallocation I/F, and whenpattern-limited area deallocation is possible with the same formatpattern (S555: YES), the first controller 110 determines whether thecopy data has the correspondence to the format pattern or not (S556).

When the copy data has the correspondence to the format pattern (S556:YES), the first controller 110 issues a command to the external storagefor deallocating the area having been allocated to the sub volume forstorage of the copy data (S557). As for any page managed by the externalstorage 200 including partially the area asked for deallocation, thepage is not deallocated but only the area asked for deallocation thereinis filled with any predetermined format data. This is because the areaof the page not asked for deallocation may include any effective data.

In step S557, together with the area deallocation command, the attributeof the copy data stored in the cache memory in the first controller 110is changed in state from dirty to clean. By changing, into the cleanstate, the attribute of the copy data stored in the cache memory in thefirst controller before data transfer into the external storage 200, thepage for storage of the copy data can be prevented from being allocatedto the external AOU volume.

Note that, when the external storage 200 is not provided with the areadeallocation I/F (S555: NO), and when the format pattern is not the sameand when pattern-limited area deallocation is not possible, and when thecopy data does not have the correspondence to the format pattern (S556:NO), the procedure returns to the flowchart of FIG. 50.

This example configured as such has the effects same as those of thefirst example. Moreover, in this example, a determination is made inadvance whether the write data or the copy data from the host has thecorrespondence to the format pattern, and if with the correspondence assuch, no page deallocation is performed, or no data transfer isperformed to the external storage. As such, any unnecessary page can beprevented from being allocated to the AOU volume with more efficiency.Note that, in this example, described mainly is the application to thefirst example, but application to the second and third examples is alsopossible.

Fifth Example

Based on FIGS. 52 and 53, a fifth example is described. In this example,as an alternative to the main storage 100, a virtualization appliance 50is used. That is, in this example, a special-purpose computer 50 is usedfor virtualizing the storage resources in the storage system.

FIG. 52 shows a storage system of this example. The virtualizationappliance 50 is connected to the host 10 via a target port 51T and overthe communications network CN1. The virtualization appliance 50 isconnected to the external storage 200 via an initiator port 51I and overthe communications network CN2. The virtualization appliance 50 is alsoconnected to the management server 20 over the communications networkCN3.

The virtualization appliance 50 is configured to include a mappingfunction 52, and a cache memory 53, for example. FIG. 53 shows thestorage configuration of this example. The virtualization appliance 50is provided with an LU layer, an LDEV layer, and an EDEV layer. Themapping function 52 manages the correlation between the LDEV 124E andthe EDEV 122E. Herein, FIG. 53 shows the one-to-one relationship betweenthe LDEV 124 in the virtualization appliance 50 and the LU 224 in theexternal storage 200, but the one-to-one relationship is surely notrestrictive. For example, a plurality of LUs 224 in the external storage200 may be coupled together in the virtualization appliance 50, and thecoupling result is used as one LDEV 124, or the LU 224 may be used as apool volume in the virtualization appliance 50.

This example configured as such also has the effects similar to those inthe first example.

Sixth Example

Based on FIGS. 54 and 55, a sixth example is described. In this example,as an alternative to the main storage 100, a virtualization switch 60 isused.

FIG. 54 shows a storage system of this example. The virtualizationswitch 60 is connected to the host 10 via a target port 61T and over thecommunications network CN1. The virtualization switch 60 is connected tothe external storage 200 via an initiator port 61I and over thecommunications network CN2. The virtualization switch 60 is alsoconnected to the management server 20 over the communications networkCN3. The virtualization switch 60 is provided with the mapping functionbut not with the cache memory.

FIG. 55 shows the storage configuration in this example. Thevirtualization switch 60 is provided with an LU layer, an LDEV layer,and an EDEV layer. The mapping function 62 manages the correlationbetween the LDEV 124E and the EDEV 122E. FIG. 55 shows the one-to-onerelationship between the LDEV 124 in the virtualization switch 60 andthe LU 224 in the external storage 200, but the one-to-one relationshipis surely not restrictive as in the fifth example.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that those skilled in the art can device numerous othermodifications and variations without departing from the scope of theinvention.

1. A storage system in which first and second storage control devicesare connected to each other for communications, the system comprising: afirst volume that is provided virtually to the first storage controldevice; a second volume that is provided virtually to the second storagecontrol device with correspondence in terms of a storage space with thefirst volume, and is accessed in response to an access request to thefirst volume; a pool section that keeps a plurality of physical storageareas for allocation to the second volume in response to a write accessrequest to the second volume; a first control section that is providedto the first storage control device, issues a command to the secondvolume in response to the access request to the first volume, andperforms data reading/writing from/to the second volume; and a secondcontrol section that is provided to the second storage control device,performs data input/output to/from the second volume in response to thecommand from the first control section, and allocates, to the secondvolume, in response to a write access request from the first controlsection, any of the plurality of physical storage areas in the poolsection not yet in use, wherein when receiving a first predeterminedcommand about the first volume, the first control section converts, fortransmission to the second control section, the first predeterminedcommand into a second predetermined command to relatively reduce a writeaccess frequency to the second volume.
 2. The storage system accordingto claim 1, wherein the first control section includes first managementinformation for use to manage a state of use of areas in the firstvolume, and second management information for use to manage a state ofuse of areas in the second volume.
 3. The storage system according toclaim 2, wherein the first and second management information eachinclude information about whether the areas are each written with data.4. The storage system according to claim 3, wherein for the data readingfrom the second volume in response to a read access request from arequest source, the first control section determines whether any of theareas designated as a read target is updated in the first volume or notbased on the first and second management information, and whendetermining that the read target area is not updated in the firstvolume, forwards predetermined format data back to the request sourcewithout accessing the second volume.
 5. The storage system according toclaim 1, wherein the first predetermined command is a format command forexecution of a format process to the first volume, and the secondpredetermined command is either another format command for execution ofthe format process to the second volume or a deallocation command fordeallocating, from the second volume, the physical storage areaallocated to the second volume.
 6. The storage system according to claim5, wherein when the second control section cannot process the secondpredetermined command, the first control section forwards, to the secondcontrol section, the write command for writing predetermined data thatis ready in advance to the second volume.
 7. The storage systemaccording to claim 1, wherein the first predetermined command is a shredcommand for execution of a shred process to the first volume, and thesecond predetermined command is either another shred command forexecution of the shred process to the second volume or a write commandfor writing of a predetermined pattern to the physical storage areaallocated to the second volume.
 8. The storage system according to claim7, wherein when the second control section cannot process the secondpredetermined command, the first control section forwards, to the secondcontrol section, the write command for writing predetermined data thatis ready in advance to the second volume.
 9. The storage systemaccording to claim 1, wherein the first predetermined command is forforming a copy pair with a third volume and the first volume provided tothe first storage control device, and for performing initial copy fromthe third to first volume, and the second predetermined command includesa deallocation command for deallocating, from the second volume, thephysical storage area allocated to the second volume, and a writecommand for data storage from the third to the first volume only to anarea of the first volume already storing any data.
 10. The storagesystem according to claim 1, wherein for forming a copy pair with athird volume and the first volume provided to the first storage controldevice, the first predetermined command is a pair resync command or apair restore command for establishing synchronization between storagedetails of the third volume and storage details of the first volume, andthe second predetermined command includes a deallocation command fordeallocating, from the second volume, the physical storage areaallocated to the second volume only for a not-yet-used area of the thirdvolume not written with any data, and a write command for data storagefrom the first to second volume only for an area of the first volumethrough with data updating.
 11. The storage system according to claim 1,wherein when the second control section cannot process the secondpredetermined command, the first control section forwards, to the secondcontrol section, an alternative command that is ready in advance for thefirst predetermined command.
 12. The storage system according to claim1, wherein the first control section can issue an Inquiry command formaking an inquiry about a configuration of the second volume, and basedon a response to the Inquiry command from the second control section,sets a relationship between the first and second volumes.
 13. Thestorage system according to claim 1, wherein the first control sectionis configured to write, when the first volume is written with data, thedata to the second volume in a unit of management area of apredetermined size, and stores format data set in advance to anyremaining portion of the management area not written with the data. 14.The storage system according to claim 1, wherein for writing of data tothe first volume, the first control section determines whether or notthe data is the same as format data that is set in advance, and whendetermining that the data is the same as the format data, sets anattribute of the data to be discardable.
 15. A method for controlling astorage system in which first and second storage control devices areconnected to each other for communications, and the storage systemincludes a first volume that is provided virtually to the first storagecontrol device, a second volume that is provided virtually to the secondstorage control device with correspondence in terms of a storage spacewith the first volume, and is accessed in response to an access requestto the first volume, and a pool section that keeps a plurality ofphysical storage areas for allocation to the second volume in responseto a write access request to the second volume, the control methodcomprising the steps of: issuing an access request to the second volumein response to the access request to the first volume, and performingdata reading/writing from/to the second volume; allocating, to thesecond volume, in response to a write access request in the accessrequest issued to the second volume for an area not yet written withdata, any of the plurality of physical storage areas in the pool sectionnot yet in use; and converting, when a first predetermined command aboutthe first volume is provided, for transmission to the second controlsection, the first predetermined command into a second predeterminedcommand to relatively reduce a write access frequency to the secondvolume.
 16. A storage system in which first and second storage controldevices are connected to each other for communications, and the storagesystem includes a first volume that is provided virtually to the firststorage control device, a second volume that is provided virtually tothe second storage control device with correspondence in terms of astorage space with the first volume, and is accessed in response to anaccess request to the first volume, and a pool section that is providedto the second storage control device, and keeps a plurality of physicalstorage areas for allocation to the second volume in response to a writeaccess request to the second volume, the system executing the steps of:making an inquiry from the first to second storage control device aboutthe information of the second volume, and based on an inquiry resultcoming from the second storage control device, setting a relationshipbetween the first and second volumes in the first storage controldevice; storing, when the write access request is issued to the firstvolume, predetermined format data into any portion in a unit ofpredetermined management area not written with write data, and issuingthe write access request to the second volume in the unit of managementarea; allocating, when the write access request is issued to the secondvolume, to any corresponding portion of the management area in thesecond volume asked for a write access, any of the plurality of physicalstorage areas not yet in use, and storing the write data to theallocated physical storage area; and when a format command is providedfor executing a format process to the first volume,
 1. forwarding, whenthe second storage control device can execute the format process to thesecond volume in response to a command coming from the first storagecontrol device, from the first to second storage control device, theformat command for making the second storage control device to executethe format process with respect to the second volume;
 2. forwarding,when the second storage control device cannot execute the format processto the second volume in response to the command coming from the firststorage control device, and when the second storage control device candeallocate, from the second volume, the physical storage area allocatedto the second volume in response to the command coming from the firststorage control device, a deallocation command from the first to secondstorage control device for deallocating the physical storage area; and3. forwarding, when the second storage control device cannot execute theformat process to the second volume in response to the command comingfrom the first storage control device, and when the second storagecontrol device cannot deallocate, from the second volume, the physicalstorage area allocated to the second volume in response to the commandcoming from the first storage control device, predetermined format datafrom the first to second storage control device, and writing thepredetermined format data to the second volume.